* [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length @ 2019-12-30 13:59 Vitaly Mireyno 2020-01-03 15:22 ` Stefan Hajnoczi ` (2 more replies) 0 siblings, 3 replies; 11+ messages in thread From: Vitaly Mireyno @ 2019-12-30 13:59 UTC (permalink / raw) To: virtio-comment; +Cc: Michael S. Tsirkin, Jason Wang This patch gives devices some level of control over the receive buffers length. The driver declares the minimum receive buffer length, and the device requests max/min buffer length ratio. This is a follow-up to the "[PATCH] virtio-net: Add equal-sized receive buffers feature" discussion: https://lists.oasis-open.org/archives/virtio-comment/201912/msg00007.html Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> --- content.tex | 41 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 39 insertions(+), 2 deletions(-) diff --git a/content.tex b/content.tex index d68cfaf..0a4cfba 100644 --- a/content.tex +++ b/content.tex @@ -2815,6 +2815,13 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control channel. +\item[VIRTIO_NET_F_RXBUF_LEN_RATIO(57)] Device requests to limit the + maximum/minimum receive buffers length ratio. + +\item[VIRTIO_NET_F_RXBUF_MIN_LEN(58)] Device requests to know the minimum + receive buffers length. Driver declares the minimum receive buffers + length. + \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact \field{hdr_len} value. Device benefits from knowing the exact header length. @@ -2861,8 +2868,8 @@ \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network \subsection{Device configuration layout}\label{sec:Device Types / Network Device / Device configuration layout} \label{sec:Device Types / Block Device / Feature bits / Device configuration layout} -Three driver-read-only configuration fields are currently defined. The \field{mac} address field -always exists (though is only valid if VIRTIO_NET_F_MAC is set), and +The driver-read-only \field{mac} address field always exists +(though is only valid if VIRTIO_NET_F_MAC is set), and \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two read-only bits (for the driver) are currently defined for the status field: VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. @@ -2882,12 +2889,22 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device VIRTIO_NET_F_MTU is set. This field specifies the maximum MTU for the driver to use. +The device-read-only field \field{min_rx_buf_len} only exists if +VIRTIO_NET_F_RXBUF_MIN_LEN is set. This field specifies the minimum receive +buffers length. + +The driver-read-only field \field{rx_buf_len_ratio} only exists if +VIRTIO_NET_F_RXBUF_LEN_RATIO is set. This field specifies the maximum/minimum receive +buffers length ratio. + \begin{lstlisting} struct virtio_net_config { u8 mac[6]; le16 status; le16 max_virtqueue_pairs; le16 mtu; + le32 min_rx_buf_len; + le16 rx_buf_len_ratio; }; \end{lstlisting} @@ -2916,6 +2933,15 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device If the driver negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act as a standby device for a primary device with the same MAC address. +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if offered. + +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the driver MUST +set \field{min_rx_buf_len}. + +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. + +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_LEN_RATIO feature if offered. + \drivernormative{\subsubsection}{Device configuration layout}{Device Types / Network Device / Device configuration layout} A driver SHOULD negotiate VIRTIO_NET_F_MAC if the device offers it. @@ -3281,6 +3307,17 @@ \subsubsection{Setting Up Receive Buffers}\label{sec:Device Types / Network Devi If VIRTIO_NET_F_MQ is negotiated, each of receiveq1\ldots receiveqN that will be used SHOULD be populated with receive buffers. +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the driver +MUST initialize all receive virtqueue descriptors \field{len} field with +the value greater than or equal to the value configured in the +\field{min_rx_buf_len} device configuration field, and allocate receive +buffers accordingly. + +If VIRTIO_NET_F_RXBUF_LEN_RATIO feature has been negotiated, the driver +MUST initialize all receive virtqueue descriptors \field{len} field with +the value less than or equal to (\field{min_rx_buf_len} * \field{rx_buf_len_ratio}), +and allocate receive buffers accordingly. + \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types / Network Device / Device Operation / Setting Up Receive Buffers} The device MUST set \field{num_buffers} to the number of descriptors used to -- This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. 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* Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2019-12-30 13:59 [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length Vitaly Mireyno @ 2020-01-03 15:22 ` Stefan Hajnoczi 2020-01-05 10:28 ` Michael S. Tsirkin 2020-01-05 10:35 ` [virtio-comment] " Michael S. Tsirkin 2020-01-20 16:24 ` [virtio-comment] " Michael S. Tsirkin 2 siblings, 1 reply; 11+ messages in thread From: Stefan Hajnoczi @ 2020-01-03 15:22 UTC (permalink / raw) To: Vitaly Mireyno; +Cc: virtio-comment, Michael S. Tsirkin, Jason Wang [-- Attachment #1: Type: text/plain, Size: 788 bytes --] On Mon, Dec 30, 2019 at 01:59:17PM +0000, Vitaly Mireyno wrote: > @@ -2916,6 +2933,15 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device > If the driver negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act > as a standby device for a primary device with the same MAC address. > > +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if offered. > + > +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the driver MUST > +set \field{min_rx_buf_len}. > + > +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. When must the driver set the fields? I guess it makes no sense to set this field after starting rx (i.e. populating the rx virtqueue)... The spec should be explicit about this. [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 488 bytes --] ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2020-01-03 15:22 ` Stefan Hajnoczi @ 2020-01-05 10:28 ` Michael S. Tsirkin 0 siblings, 0 replies; 11+ messages in thread From: Michael S. Tsirkin @ 2020-01-05 10:28 UTC (permalink / raw) To: Stefan Hajnoczi; +Cc: Vitaly Mireyno, virtio-comment, Jason Wang On Fri, Jan 03, 2020 at 03:22:44PM +0000, Stefan Hajnoczi wrote: > On Mon, Dec 30, 2019 at 01:59:17PM +0000, Vitaly Mireyno wrote: > > @@ -2916,6 +2933,15 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device > > If the driver negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act > > as a standby device for a primary device with the same MAC address. > > > > +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if offered. > > + > > +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the driver MUST > > +set \field{min_rx_buf_len}. > > + > > +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. > > When must the driver set the fields? I guess it makes no sense to set > this field after starting rx (i.e. populating the rx virtqueue)... The > spec should be explicit about this. If we are going to keep it static then I think the best time is before features ok. This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/ ^ permalink raw reply [flat|nested] 11+ messages in thread
* [virtio-comment] Re: [PATCH] virtio-net: Add an optional device control over the receive buffers length 2019-12-30 13:59 [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length Vitaly Mireyno 2020-01-03 15:22 ` Stefan Hajnoczi @ 2020-01-05 10:35 ` Michael S. Tsirkin 2020-01-20 16:24 ` [virtio-comment] " Michael S. Tsirkin 2 siblings, 0 replies; 11+ messages in thread From: Michael S. Tsirkin @ 2020-01-05 10:35 UTC (permalink / raw) To: Vitaly Mireyno; +Cc: virtio-comment, Jason Wang On Mon, Dec 30, 2019 at 01:59:17PM +0000, Vitaly Mireyno wrote: > This patch gives devices some level of control over the receive buffers length. > The driver declares the minimum receive buffer length, and the device requests max/min buffer length ratio. > This is a follow-up to the "[PATCH] virtio-net: Add equal-sized receive buffers feature" discussion: https://lists.oasis-open.org/archives/virtio-comment/201912/msg00007.html > > > Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> > --- > content.tex | 41 +++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 39 insertions(+), 2 deletions(-) > > diff --git a/content.tex b/content.tex > index d68cfaf..0a4cfba 100644 > --- a/content.tex > +++ b/content.tex > @@ -2815,6 +2815,13 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits > \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control > channel. > > +\item[VIRTIO_NET_F_RXBUF_LEN_RATIO(57)] Device requests to limit the > + maximum/minimum receive buffers length ratio. > + So VIRTIO_NET_F_RXBUF_LEN_RATIO only makes sense with VIRTIO_NET_F_RXBUF_MIN_LEN, right? I think we can just use a single feature bit then, and just set ratio to 0 to mean "infinity". > +\item[VIRTIO_NET_F_RXBUF_MIN_LEN(58)] Device requests to know the minimum > + receive buffers length. Driver declares the minimum receive buffers > + length. > + > \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact \field{hdr_len} > value. Device benefits from knowing the exact header length. > > @@ -2861,8 +2868,8 @@ \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network > \subsection{Device configuration layout}\label{sec:Device Types / Network Device / Device configuration layout} > \label{sec:Device Types / Block Device / Feature bits / Device configuration layout} > > -Three driver-read-only configuration fields are currently defined. The \field{mac} address field > -always exists (though is only valid if VIRTIO_NET_F_MAC is set), and > +The driver-read-only \field{mac} address field always exists > +(though is only valid if VIRTIO_NET_F_MAC is set), and > \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two > read-only bits (for the driver) are currently defined for the status field: > VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. > @@ -2882,12 +2889,22 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device > VIRTIO_NET_F_MTU is set. This field specifies the maximum MTU for the driver to > use. > > +The device-read-only field \field{min_rx_buf_len} only exists if > +VIRTIO_NET_F_RXBUF_MIN_LEN is set. This field specifies the minimum receive > +buffers length. > + > +The driver-read-only field \field{rx_buf_len_ratio} only exists if > +VIRTIO_NET_F_RXBUF_LEN_RATIO is set. This field specifies the maximum/minimum receive > +buffers length ratio. Actually shouldn't all of these always exist and only be valid if a flag is set? I think existing text should be fixed too. > + > \begin{lstlisting} > struct virtio_net_config { > u8 mac[6]; > le16 status; > le16 max_virtqueue_pairs; > le16 mtu; > + le32 min_rx_buf_len; > + le16 rx_buf_len_ratio; > }; > \end{lstlisting} > > @@ -2916,6 +2933,15 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device > If the driver negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act > as a standby device for a primary device with the same MAC address. > > +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if offered. > + > +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the driver MUST > +set \field{min_rx_buf_len}. > + > +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. > + > +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_LEN_RATIO feature if offered. > + > \drivernormative{\subsubsection}{Device configuration layout}{Device Types / Network Device / Device configuration layout} > > A driver SHOULD negotiate VIRTIO_NET_F_MAC if the device offers it. > @@ -3281,6 +3307,17 @@ \subsubsection{Setting Up Receive Buffers}\label{sec:Device Types / Network Devi > If VIRTIO_NET_F_MQ is negotiated, each of receiveq1\ldots receiveqN > that will be used SHOULD be populated with receive buffers. > > +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the driver > +MUST initialize all receive virtqueue descriptors \field{len} field with > +the value greater than or equal to the value configured in the > +\field{min_rx_buf_len} device configuration field, and allocate receive > +buffers accordingly. I think above should talk about buffer length, discussion about descriptors doesn't belong in devices, it's a way to describe buffers. If we want to limit descriptors per rx buffer, I think it's a separate feature similar to max_sg for blk/scsi. > +If VIRTIO_NET_F_RXBUF_LEN_RATIO feature has been negotiated, the driver > +MUST initialize all receive virtqueue descriptors \field{len} field with > +the value less than or equal to (\field{min_rx_buf_len} * \field{rx_buf_len_ratio}), > +and allocate receive buffers accordingly. > + > \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types / Network Device / Device Operation / Setting Up Receive Buffers} > > The device MUST set \field{num_buffers} to the number of descriptors used to > -- This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/ ^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2019-12-30 13:59 [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length Vitaly Mireyno 2020-01-03 15:22 ` Stefan Hajnoczi 2020-01-05 10:35 ` [virtio-comment] " Michael S. Tsirkin @ 2020-01-20 16:24 ` Michael S. Tsirkin 2020-01-22 16:06 ` [virtio-comment] RE: [EXT] " Vitaly Mireyno 2 siblings, 1 reply; 11+ messages in thread From: Michael S. Tsirkin @ 2020-01-20 16:24 UTC (permalink / raw) To: Vitaly Mireyno; +Cc: virtio-comment, Jason Wang On Mon, Dec 30, 2019 at 01:59:17PM +0000, Vitaly Mireyno wrote: > This patch gives devices some level of control over the receive buffers length. > The driver declares the minimum receive buffer length, and the device requests max/min buffer length ratio. > This is a follow-up to the "[PATCH] virtio-net: Add equal-sized receive buffers feature" discussion: https://lists.oasis-open.org/archives/virtio-comment/201912/msg00007.html > > > Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> > --- > content.tex | 41 +++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 39 insertions(+), 2 deletions(-) > > diff --git a/content.tex b/content.tex > index d68cfaf..0a4cfba 100644 > --- a/content.tex > +++ b/content.tex > @@ -2815,6 +2815,13 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits > \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control > channel. > > +\item[VIRTIO_NET_F_RXBUF_LEN_RATIO(57)] Device requests to limit the > + maximum/minimum receive buffers length ratio. > + > +\item[VIRTIO_NET_F_RXBUF_MIN_LEN(58)] Device requests to know the minimum > + receive buffers length. Driver declares the minimum receive buffers > + length. > + > \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact \field{hdr_len} > value. Device benefits from knowing the exact header length. > So I am wondering, when we are switching from regular skbs to XDP, all buffers become 4K. When we switch back, we get variability again. All the while some old buffers can be outstanding. How will we handle this? > @@ -2861,8 +2868,8 @@ \subsubsection{Legacy Interface: Feature bits}\label{sec:Device Types / Network > \subsection{Device configuration layout}\label{sec:Device Types / Network Device / Device configuration layout} > \label{sec:Device Types / Block Device / Feature bits / Device configuration layout} > > -Three driver-read-only configuration fields are currently defined. The \field{mac} address field > -always exists (though is only valid if VIRTIO_NET_F_MAC is set), and > +The driver-read-only \field{mac} address field always exists > +(though is only valid if VIRTIO_NET_F_MAC is set), and > \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two > read-only bits (for the driver) are currently defined for the status field: > VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. > @@ -2882,12 +2889,22 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device > VIRTIO_NET_F_MTU is set. This field specifies the maximum MTU for the driver to > use. > > +The device-read-only field \field{min_rx_buf_len} only exists if > +VIRTIO_NET_F_RXBUF_MIN_LEN is set. This field specifies the minimum receive > +buffers length. > + > +The driver-read-only field \field{rx_buf_len_ratio} only exists if > +VIRTIO_NET_F_RXBUF_LEN_RATIO is set. This field specifies the maximum/minimum receive > +buffers length ratio. > + > \begin{lstlisting} > struct virtio_net_config { > u8 mac[6]; > le16 status; > le16 max_virtqueue_pairs; > le16 mtu; > + le32 min_rx_buf_len; > + le16 rx_buf_len_ratio; > }; > \end{lstlisting} > > @@ -2916,6 +2933,15 @@ \subsection{Device configuration layout}\label{sec:Device Types / Network Device > If the driver negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act > as a standby device for a primary device with the same MAC address. > > +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if offered. > + > +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the driver MUST > +set \field{min_rx_buf_len}. > + > +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. > + > +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_LEN_RATIO feature if offered. > + > \drivernormative{\subsubsection}{Device configuration layout}{Device Types / Network Device / Device configuration layout} > > A driver SHOULD negotiate VIRTIO_NET_F_MAC if the device offers it. > @@ -3281,6 +3307,17 @@ \subsubsection{Setting Up Receive Buffers}\label{sec:Device Types / Network Devi > If VIRTIO_NET_F_MQ is negotiated, each of receiveq1\ldots receiveqN > that will be used SHOULD be populated with receive buffers. > > +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the driver > +MUST initialize all receive virtqueue descriptors \field{len} field with > +the value greater than or equal to the value configured in the > +\field{min_rx_buf_len} device configuration field, and allocate receive > +buffers accordingly. > + > +If VIRTIO_NET_F_RXBUF_LEN_RATIO feature has been negotiated, the driver > +MUST initialize all receive virtqueue descriptors \field{len} field with > +the value less than or equal to (\field{min_rx_buf_len} * \field{rx_buf_len_ratio}), > +and allocate receive buffers accordingly. > + > \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types / Network Device / Device Operation / Setting Up Receive Buffers} > > The device MUST set \field{num_buffers} to the number of descriptors used to > -- > > This publicly archived list offers a means to provide input to the > OASIS Virtual I/O Device (VIRTIO) TC. > > In order to verify user consent to the Feedback License terms and > to minimize spam in the list archive, subscription is required > before posting. > > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > List help: virtio-comment-help@lists.oasis-open.org > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists > Committee: https://www.oasis-open.org/committees/virtio/ > Join OASIS: https://www.oasis-open.org/join/ This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/ ^ permalink raw reply [flat|nested] 11+ messages in thread
* [virtio-comment] RE: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2020-01-20 16:24 ` [virtio-comment] " Michael S. Tsirkin @ 2020-01-22 16:06 ` Vitaly Mireyno 2020-01-23 6:55 ` [virtio-comment] " Michael S. Tsirkin 0 siblings, 1 reply; 11+ messages in thread From: Vitaly Mireyno @ 2020-01-22 16:06 UTC (permalink / raw) To: Michael S. Tsirkin; +Cc: virtio-comment, Jason Wang >-----Original Message----- >From: Michael S. Tsirkin <mst@redhat.com> >Sent: Monday, 20 January, 2020 18:25 >To: Vitaly Mireyno <vmireyno@marvell.com> >Cc: virtio-comment@lists.oasis-open.org; Jason Wang ><jasowang@redhat.com> >Subject: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device >control over the receive buffers length > >External Email > >---------------------------------------------------------------------- >On Mon, Dec 30, 2019 at 01:59:17PM +0000, Vitaly Mireyno wrote: >> This patch gives devices some level of control over the receive buffers >length. >> The driver declares the minimum receive buffer length, and the device >requests max/min buffer length ratio. >> This is a follow-up to the "[PATCH] virtio-net: Add equal-sized >> receive buffers feature" discussion: >> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.oasis-2Dope >> n.org_archives_virtio- >2Dcomment_201912_msg00007.html&d=DwIFAg&c=nKjWec >> >2b6R0mOyPaz7xtfQ&r=lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI& >m=jrQgZ >> - >iN3QnvFqxQQkoPTmztJRTNCXTF2dz68TEV0cA&s=pDtISMJpw1N9ohot9fluo1N >j1X2s1 >> J_sEVJGg2uwkZk&e= >> >> >> Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> >> --- >> content.tex | 41 +++++++++++++++++++++++++++++++++++++++-- >> 1 file changed, 39 insertions(+), 2 deletions(-) >> >> diff --git a/content.tex b/content.tex index d68cfaf..0a4cfba 100644 >> --- a/content.tex >> +++ b/content.tex >> @@ -2815,6 +2815,13 @@ \subsection{Feature bits}\label{sec:Device >> Types / Network Device / Feature bits >\item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through >control >> channel. >> >> +\item[VIRTIO_NET_F_RXBUF_LEN_RATIO(57)] Device requests to limit the >> + maximum/minimum receive buffers length ratio. >> + >> +\item[VIRTIO_NET_F_RXBUF_MIN_LEN(58)] Device requests to know the >minimum >> + receive buffers length. Driver declares the minimum receive buffers >> + length. >> + >> \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact >\field{hdr_len} >> value. Device benefits from knowing the exact header length. >> > >So I am wondering, when we are switching from regular skbs to XDP, all >buffers become 4K. When we switch back, we get variability again. >All the while some old buffers can be outstanding. > >How will we handle this? > The feature limits the flexibility of the driver to set the descriptors length. It doesn't limit the actual buffer allocation size. So if XDP requires a larger headroom, I don't see a problem. Please excuse my ignorance, but what do you mean by "all buffers become 4K"? > >> @@ -2861,8 +2868,8 @@ \subsubsection{Legacy Interface: Feature >> bits}\label{sec:Device Types / Network \subsection{Device >> configuration layout}\label{sec:Device Types / Network Device / Device >> configuration layout} \label{sec:Device Types / Block Device / >> Feature bits / Device configuration layout} >> >> -Three driver-read-only configuration fields are currently defined. >> The \field{mac} address field -always exists (though is only valid if >> VIRTIO_NET_F_MAC is set), and >> +The driver-read-only \field{mac} address field always exists (though >> +is only valid if VIRTIO_NET_F_MAC is set), and >> \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two >> read-only bits (for the driver) are currently defined for the status field: >> VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. >> @@ -2882,12 +2889,22 @@ \subsection{Device configuration >> layout}\label{sec:Device Types / Network Device VIRTIO_NET_F_MTU is >> set. This field specifies the maximum MTU for the driver to use. >> >> +The device-read-only field \field{min_rx_buf_len} only exists if >> +VIRTIO_NET_F_RXBUF_MIN_LEN is set. This field specifies the minimum >> +receive buffers length. >> + >> +The driver-read-only field \field{rx_buf_len_ratio} only exists if >> +VIRTIO_NET_F_RXBUF_LEN_RATIO is set. This field specifies the >> +maximum/minimum receive buffers length ratio. >> + >> \begin{lstlisting} >> struct virtio_net_config { >> u8 mac[6]; >> le16 status; >> le16 max_virtqueue_pairs; >> le16 mtu; >> + le32 min_rx_buf_len; >> + le16 rx_buf_len_ratio; >> }; >> \end{lstlisting} >> >> @@ -2916,6 +2933,15 @@ \subsection{Device configuration >> layout}\label{sec:Device Types / Network Device If the driver >> negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act as a >standby device for a primary device with the same MAC address. >> >> +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if >offered. >> + >> +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the >driver >> +MUST set \field{min_rx_buf_len}. >> + >> +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. >> + >> +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_LEN_RATIO feature if >offered. >> + >> \drivernormative{\subsubsection}{Device configuration layout}{Device >> Types / Network Device / Device configuration layout} >> >> A driver SHOULD negotiate VIRTIO_NET_F_MAC if the device offers it. >> @@ -3281,6 +3307,17 @@ \subsubsection{Setting Up Receive >> Buffers}\label{sec:Device Types / Network Devi If VIRTIO_NET_F_MQ is >> negotiated, each of receiveq1\ldots receiveqN that will be used SHOULD be >populated with receive buffers. >> >> +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the >driver >> +MUST initialize all receive virtqueue descriptors \field{len} field >> +with the value greater than or equal to the value configured in the >> +\field{min_rx_buf_len} device configuration field, and allocate >> +receive buffers accordingly. >> + >> +If VIRTIO_NET_F_RXBUF_LEN_RATIO feature has been negotiated, the >> +driver MUST initialize all receive virtqueue descriptors \field{len} >> +field with the value less than or equal to (\field{min_rx_buf_len} * >> +\field{rx_buf_len_ratio}), and allocate receive buffers accordingly. >> + >> \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types >> / Network Device / Device Operation / Setting Up Receive Buffers} >> >> The device MUST set \field{num_buffers} to the number of descriptors >> used to >> -- >> >> This publicly archived list offers a means to provide input to the >> OASIS Virtual I/O Device (VIRTIO) TC. >> >> In order to verify user consent to the Feedback License terms and to >> minimize spam in the list archive, subscription is required before >> posting. >> >> Subscribe: virtio-comment-subscribe@lists.oasis-open.org >> Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org >> List help: virtio-comment-help@lists.oasis-open.org >> List archive: >> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.oasis-2Dope >> n.org_archives_virtio- >2Dcomment_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=l >> DHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- >iN3QnvFqxQQkoPTmztJ >> RTNCXTF2dz68TEV0cA&s=yHWSFWSoze0yJhs- >YBtijO34uqnnV0LoPfizi0miMNQ&e= >> Feedback License: >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- >2Dopen. >> org_who_ipr_feedback- >5Flicense.pdf&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r >> =lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- >iN3QnvFqxQQkoPTmz >> >tJRTNCXTF2dz68TEV0cA&s=19yavBBd2Ai05CwKnyFOLRNlBnNAtmpKVsTMB6sI >TRE&e= >> List Guidelines: >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- >2Dopen. >> org_policies-2Dguidelines_mailing- >2Dlists&d=DwIFAg&c=nKjWec2b6R0mOyPaz >> 7xtfQ&r=lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- >iN3QnvFqxQ >> QkoPTmztJRTNCXTF2dz68TEV0cA&s=3bbeWIoIuAK6RwARN2q- >t9hPTDAKbwOJ8fMRykpq >> ryk&e= >> Committee: >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- >2Dopen. >> >org_committees_virtio_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=lDHJ2F >W52oJ >> 3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- >iN3QnvFqxQQkoPTmztJRTNCXTF2dz >> 68TEV0cA&s=U8z-sIxuNy_keXvWYnlIzloNziRKqC1pxOG-x3Hy6SY&e= >> Join OASIS: >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- >2Dopen. >> >org_join_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=lDHJ2FW52oJ3lqqsAr >gFRdce >> vq01tbLQAw4A_NO7xgI&m=jrQgZ- >iN3QnvFqxQQkoPTmztJRTNCXTF2dz68TEV0cA&s=C4 >> SQkiR2V1N3I_ri_7fwSiHmcVRNPp2FnVA4gR0-cgM&e= This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/ ^ permalink raw reply [flat|nested] 11+ messages in thread
* [virtio-comment] Re: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2020-01-22 16:06 ` [virtio-comment] RE: [EXT] " Vitaly Mireyno @ 2020-01-23 6:55 ` Michael S. Tsirkin 2020-01-23 7:10 ` Jason Wang 0 siblings, 1 reply; 11+ messages in thread From: Michael S. Tsirkin @ 2020-01-23 6:55 UTC (permalink / raw) To: Vitaly Mireyno; +Cc: virtio-comment, Jason Wang On Wed, Jan 22, 2020 at 04:06:30PM +0000, Vitaly Mireyno wrote: > > > >-----Original Message----- > >From: Michael S. Tsirkin <mst@redhat.com> > >Sent: Monday, 20 January, 2020 18:25 > >To: Vitaly Mireyno <vmireyno@marvell.com> > >Cc: virtio-comment@lists.oasis-open.org; Jason Wang > ><jasowang@redhat.com> > >Subject: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device > >control over the receive buffers length > > > >External Email > > > >---------------------------------------------------------------------- > >On Mon, Dec 30, 2019 at 01:59:17PM +0000, Vitaly Mireyno wrote: > >> This patch gives devices some level of control over the receive buffers > >length. > >> The driver declares the minimum receive buffer length, and the device > >requests max/min buffer length ratio. > >> This is a follow-up to the "[PATCH] virtio-net: Add equal-sized > >> receive buffers feature" discussion: > >> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.oasis-2Dope > >> n.org_archives_virtio- > >2Dcomment_201912_msg00007.html&d=DwIFAg&c=nKjWec > >> > >2b6R0mOyPaz7xtfQ&r=lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI& > >m=jrQgZ > >> - > >iN3QnvFqxQQkoPTmztJRTNCXTF2dz68TEV0cA&s=pDtISMJpw1N9ohot9fluo1N > >j1X2s1 > >> J_sEVJGg2uwkZk&e= > >> > >> > >> Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> > >> --- > >> content.tex | 41 +++++++++++++++++++++++++++++++++++++++-- > >> 1 file changed, 39 insertions(+), 2 deletions(-) > >> > >> diff --git a/content.tex b/content.tex index d68cfaf..0a4cfba 100644 > >> --- a/content.tex > >> +++ b/content.tex > >> @@ -2815,6 +2815,13 @@ \subsection{Feature bits}\label{sec:Device > >> Types / Network Device / Feature bits > >\item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through > >control > >> channel. > >> > >> +\item[VIRTIO_NET_F_RXBUF_LEN_RATIO(57)] Device requests to limit the > >> + maximum/minimum receive buffers length ratio. > >> + > >> +\item[VIRTIO_NET_F_RXBUF_MIN_LEN(58)] Device requests to know the > >minimum > >> + receive buffers length. Driver declares the minimum receive buffers > >> + length. > >> + > >> \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact > >\field{hdr_len} > >> value. Device benefits from knowing the exact header length. > >> > > > >So I am wondering, when we are switching from regular skbs to XDP, all > >buffers become 4K. When we switch back, we get variability again. > >All the while some old buffers can be outstanding. > > > >How will we handle this? > > > > The feature limits the flexibility of the driver to set the descriptors length. > It doesn't limit the actual buffer allocation size. So if XDP requires a larger headroom, I don't see a problem. Please excuse my ignorance, but what do you mean by "all buffers become 4K"? So linux can switch between skb and XDP mode. In skb mode buffer size varies, it works by merging multiple buffers. In XDP a single buffer is made big enough to hold the whole packet. Length is fixed. If we are in XDP mode but buffer was added while in skb mode, or vice versa, we recover generally by copying data to the correct buffer. This is a temporary slowdown - better than dropping packets. So let's assume the device ratio is 1. I guess while in XDP mode, we'll write XDP buffer length into this field. But in skb mode, we can make the buffer smaller. This implies driver needs to change the min_rx_buf_len? > > > >> @@ -2861,8 +2868,8 @@ \subsubsection{Legacy Interface: Feature > >> bits}\label{sec:Device Types / Network \subsection{Device > >> configuration layout}\label{sec:Device Types / Network Device / Device > >> configuration layout} \label{sec:Device Types / Block Device / > >> Feature bits / Device configuration layout} > >> > >> -Three driver-read-only configuration fields are currently defined. > >> The \field{mac} address field -always exists (though is only valid if > >> VIRTIO_NET_F_MAC is set), and > >> +The driver-read-only \field{mac} address field always exists (though > >> +is only valid if VIRTIO_NET_F_MAC is set), and > >> \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two > >> read-only bits (for the driver) are currently defined for the status field: > >> VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. > >> @@ -2882,12 +2889,22 @@ \subsection{Device configuration > >> layout}\label{sec:Device Types / Network Device VIRTIO_NET_F_MTU is > >> set. This field specifies the maximum MTU for the driver to use. > >> > >> +The device-read-only field \field{min_rx_buf_len} only exists if > >> +VIRTIO_NET_F_RXBUF_MIN_LEN is set. This field specifies the minimum > >> +receive buffers length. > >> + > >> +The driver-read-only field \field{rx_buf_len_ratio} only exists if > >> +VIRTIO_NET_F_RXBUF_LEN_RATIO is set. This field specifies the > >> +maximum/minimum receive buffers length ratio. > >> + Config space access is from point of view of driver (it's part of device so it does not make sense to talk about device reading it). The point is driver is not supposed to read it, right? So s/device-read-only/driver-write-only/ or better "write-only for driver". > >> \begin{lstlisting} > >> struct virtio_net_config { > >> u8 mac[6]; > >> le16 status; > >> le16 max_virtqueue_pairs; > >> le16 mtu; > >> + le32 min_rx_buf_len; > >> + le16 rx_buf_len_ratio; > >> }; > >> \end{lstlisting} > >> > >> @@ -2916,6 +2933,15 @@ \subsection{Device configuration > >> layout}\label{sec:Device Types / Network Device If the driver > >> negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act as a > >standby device for a primary device with the same MAC address. > >> > >> +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if > >offered. > >> + > >> +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the > >driver > >> +MUST set \field{min_rx_buf_len}. > >> + > >> +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. > >> + > >> +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_LEN_RATIO feature if > >offered. > >> + > >> \drivernormative{\subsubsection}{Device configuration layout}{Device > >> Types / Network Device / Device configuration layout} > >> > >> A driver SHOULD negotiate VIRTIO_NET_F_MAC if the device offers it. > >> @@ -3281,6 +3307,17 @@ \subsubsection{Setting Up Receive > >> Buffers}\label{sec:Device Types / Network Devi If VIRTIO_NET_F_MQ is > >> negotiated, each of receiveq1\ldots receiveqN that will be used SHOULD be > >populated with receive buffers. > >> > >> +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the > >driver > >> +MUST initialize all receive virtqueue descriptors \field{len} field > >> +with the value greater than or equal to the value configured in the > >> +\field{min_rx_buf_len} device configuration field, and allocate > >> +receive buffers accordingly. > >> + > >> +If VIRTIO_NET_F_RXBUF_LEN_RATIO feature has been negotiated, the > >> +driver MUST initialize all receive virtqueue descriptors \field{len} > >> +field with the value less than or equal to (\field{min_rx_buf_len} * > >> +\field{rx_buf_len_ratio}), and allocate receive buffers accordingly. > >> + > >> \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types > >> / Network Device / Device Operation / Setting Up Receive Buffers} > >> > >> The device MUST set \field{num_buffers} to the number of descriptors > >> used to > >> -- > >> > >> This publicly archived list offers a means to provide input to the > >> OASIS Virtual I/O Device (VIRTIO) TC. > >> > >> In order to verify user consent to the Feedback License terms and to > >> minimize spam in the list archive, subscription is required before > >> posting. > >> > >> Subscribe: virtio-comment-subscribe@lists.oasis-open.org > >> Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > >> List help: virtio-comment-help@lists.oasis-open.org > >> List archive: > >> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.oasis-2Dope > >> n.org_archives_virtio- > >2Dcomment_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=l > >> DHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- > >iN3QnvFqxQQkoPTmztJ > >> RTNCXTF2dz68TEV0cA&s=yHWSFWSoze0yJhs- > >YBtijO34uqnnV0LoPfizi0miMNQ&e= > >> Feedback License: > >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- > >2Dopen. > >> org_who_ipr_feedback- > >5Flicense.pdf&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r > >> =lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- > >iN3QnvFqxQQkoPTmz > >> > >tJRTNCXTF2dz68TEV0cA&s=19yavBBd2Ai05CwKnyFOLRNlBnNAtmpKVsTMB6sI > >TRE&e= > >> List Guidelines: > >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- > >2Dopen. > >> org_policies-2Dguidelines_mailing- > >2Dlists&d=DwIFAg&c=nKjWec2b6R0mOyPaz > >> 7xtfQ&r=lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- > >iN3QnvFqxQ > >> QkoPTmztJRTNCXTF2dz68TEV0cA&s=3bbeWIoIuAK6RwARN2q- > >t9hPTDAKbwOJ8fMRykpq > >> ryk&e= > >> Committee: > >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- > >2Dopen. > >> > >org_committees_virtio_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=lDHJ2F > >W52oJ > >> 3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- > >iN3QnvFqxQQkoPTmztJRTNCXTF2dz > >> 68TEV0cA&s=U8z-sIxuNy_keXvWYnlIzloNziRKqC1pxOG-x3Hy6SY&e= > >> Join OASIS: > >> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- > >2Dopen. > >> > >org_join_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=lDHJ2FW52oJ3lqqsAr > >gFRdce > >> vq01tbLQAw4A_NO7xgI&m=jrQgZ- > >iN3QnvFqxQQkoPTmztJRTNCXTF2dz68TEV0cA&s=C4 > >> SQkiR2V1N3I_ri_7fwSiHmcVRNPp2FnVA4gR0-cgM&e= This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/ ^ permalink raw reply [flat|nested] 11+ messages in thread
* [virtio-comment] Re: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2020-01-23 6:55 ` [virtio-comment] " Michael S. Tsirkin @ 2020-01-23 7:10 ` Jason Wang 2020-01-23 7:46 ` Michael S. Tsirkin 0 siblings, 1 reply; 11+ messages in thread From: Jason Wang @ 2020-01-23 7:10 UTC (permalink / raw) To: Michael S. Tsirkin, Vitaly Mireyno; +Cc: virtio-comment On 2020/1/23 下午2:55, Michael S. Tsirkin wrote: > On Wed, Jan 22, 2020 at 04:06:30PM +0000, Vitaly Mireyno wrote: >> >>> -----Original Message----- >>> From: Michael S. Tsirkin <mst@redhat.com> >>> Sent: Monday, 20 January, 2020 18:25 >>> To: Vitaly Mireyno <vmireyno@marvell.com> >>> Cc: virtio-comment@lists.oasis-open.org; Jason Wang >>> <jasowang@redhat.com> >>> Subject: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device >>> control over the receive buffers length >>> >>> External Email >>> >>> ---------------------------------------------------------------------- >>> On Mon, Dec 30, 2019 at 01:59:17PM +0000, Vitaly Mireyno wrote: >>>> This patch gives devices some level of control over the receive buffers >>> length. >>>> The driver declares the minimum receive buffer length, and the device >>> requests max/min buffer length ratio. >>>> This is a follow-up to the "[PATCH] virtio-net: Add equal-sized >>>> receive buffers feature" discussion: >>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.oasis-2Dope >>>> n.org_archives_virtio- >>> 2Dcomment_201912_msg00007.html&d=DwIFAg&c=nKjWec >>> 2b6R0mOyPaz7xtfQ&r=lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI& >>> m=jrQgZ >>>> - >>> iN3QnvFqxQQkoPTmztJRTNCXTF2dz68TEV0cA&s=pDtISMJpw1N9ohot9fluo1N >>> j1X2s1 >>>> J_sEVJGg2uwkZk&e= >>>> >>>> >>>> Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> >>>> --- >>>> content.tex | 41 +++++++++++++++++++++++++++++++++++++++-- >>>> 1 file changed, 39 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/content.tex b/content.tex index d68cfaf..0a4cfba 100644 >>>> --- a/content.tex >>>> +++ b/content.tex >>>> @@ -2815,6 +2815,13 @@ \subsection{Feature bits}\label{sec:Device >>>> Types / Network Device / Feature bits >>> \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through >>> control >>>> channel. >>>> >>>> +\item[VIRTIO_NET_F_RXBUF_LEN_RATIO(57)] Device requests to limit the >>>> + maximum/minimum receive buffers length ratio. >>>> + >>>> +\item[VIRTIO_NET_F_RXBUF_MIN_LEN(58)] Device requests to know the >>> minimum >>>> + receive buffers length. Driver declares the minimum receive buffers >>>> + length. >>>> + >>>> \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact >>> \field{hdr_len} >>>> value. Device benefits from knowing the exact header length. >>>> >>> So I am wondering, when we are switching from regular skbs to XDP, all >>> buffers become 4K. When we switch back, we get variability again. >>> All the while some old buffers can be outstanding. >>> >>> How will we handle this? >>> >> The feature limits the flexibility of the driver to set the descriptors length. >> It doesn't limit the actual buffer allocation size. So if XDP requires a larger headroom, I don't see a problem. Please excuse my ignorance, but what do you mean by "all buffers become 4K"? > So linux can switch between skb and XDP mode. In skb mode buffer size > varies, it works by merging multiple buffers. In XDP a single buffer > is made big enough to hold the whole packet. Length is fixed. > > If we are in XDP mode but buffer was added while in skb mode, > or vice versa, we recover generally by copying data to > the correct buffer. This is a temporary slowdown - > better than dropping packets. > > So let's assume the device ratio is 1. > I guess while in XDP mode, we'll write XDP buffer length into > this field. But in skb mode, we can make the buffer smaller. > This implies driver needs to change the min_rx_buf_len? I'm not sure I get here. The header room should be invisible from device point of view I think. Thanks > > > >>>> @@ -2861,8 +2868,8 @@ \subsubsection{Legacy Interface: Feature >>>> bits}\label{sec:Device Types / Network \subsection{Device >>>> configuration layout}\label{sec:Device Types / Network Device / Device >>>> configuration layout} \label{sec:Device Types / Block Device / >>>> Feature bits / Device configuration layout} >>>> >>>> -Three driver-read-only configuration fields are currently defined. >>>> The \field{mac} address field -always exists (though is only valid if >>>> VIRTIO_NET_F_MAC is set), and >>>> +The driver-read-only \field{mac} address field always exists (though >>>> +is only valid if VIRTIO_NET_F_MAC is set), and >>>> \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two >>>> read-only bits (for the driver) are currently defined for the status field: >>>> VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. >>>> @@ -2882,12 +2889,22 @@ \subsection{Device configuration >>>> layout}\label{sec:Device Types / Network Device VIRTIO_NET_F_MTU is >>>> set. This field specifies the maximum MTU for the driver to use. >>>> >>>> +The device-read-only field \field{min_rx_buf_len} only exists if >>>> +VIRTIO_NET_F_RXBUF_MIN_LEN is set. This field specifies the minimum >>>> +receive buffers length. >>>> + >>>> +The driver-read-only field \field{rx_buf_len_ratio} only exists if >>>> +VIRTIO_NET_F_RXBUF_LEN_RATIO is set. This field specifies the >>>> +maximum/minimum receive buffers length ratio. >>>> + > Config space access is from point of view of driver (it's part of device > so it does not make sense to talk about device reading it). > The point is driver is not supposed to read it, right? > So s/device-read-only/driver-write-only/ or better "write-only for > driver". > >>>> \begin{lstlisting} >>>> struct virtio_net_config { >>>> u8 mac[6]; >>>> le16 status; >>>> le16 max_virtqueue_pairs; >>>> le16 mtu; >>>> + le32 min_rx_buf_len; >>>> + le16 rx_buf_len_ratio; >>>> }; >>>> \end{lstlisting} >>>> >>>> @@ -2916,6 +2933,15 @@ \subsection{Device configuration >>>> layout}\label{sec:Device Types / Network Device If the driver >>>> negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act as a >>> standby device for a primary device with the same MAC address. >>>> +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if >>> offered. >>>> + >>>> +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the >>> driver >>>> +MUST set \field{min_rx_buf_len}. >>>> + >>>> +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. >>>> + >>>> +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_LEN_RATIO feature if >>> offered. >>>> + >>>> \drivernormative{\subsubsection}{Device configuration layout}{Device >>>> Types / Network Device / Device configuration layout} >>>> >>>> A driver SHOULD negotiate VIRTIO_NET_F_MAC if the device offers it. >>>> @@ -3281,6 +3307,17 @@ \subsubsection{Setting Up Receive >>>> Buffers}\label{sec:Device Types / Network Devi If VIRTIO_NET_F_MQ is >>>> negotiated, each of receiveq1\ldots receiveqN that will be used SHOULD be >>> populated with receive buffers. >>>> +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the >>> driver >>>> +MUST initialize all receive virtqueue descriptors \field{len} field >>>> +with the value greater than or equal to the value configured in the >>>> +\field{min_rx_buf_len} device configuration field, and allocate >>>> +receive buffers accordingly. >>>> + >>>> +If VIRTIO_NET_F_RXBUF_LEN_RATIO feature has been negotiated, the >>>> +driver MUST initialize all receive virtqueue descriptors \field{len} >>>> +field with the value less than or equal to (\field{min_rx_buf_len} * >>>> +\field{rx_buf_len_ratio}), and allocate receive buffers accordingly. >>>> + >>>> \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types >>>> / Network Device / Device Operation / Setting Up Receive Buffers} >>>> >>>> The device MUST set \field{num_buffers} to the number of descriptors >>>> used to >>>> -- >>>> >>>> This publicly archived list offers a means to provide input to the >>>> OASIS Virtual I/O Device (VIRTIO) TC. >>>> >>>> In order to verify user consent to the Feedback License terms and to >>>> minimize spam in the list archive, subscription is required before >>>> posting. >>>> >>>> Subscribe: virtio-comment-subscribe@lists.oasis-open.org >>>> Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org >>>> List help: virtio-comment-help@lists.oasis-open.org >>>> List archive: >>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.oasis-2Dope >>>> n.org_archives_virtio- >>> 2Dcomment_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=l >>>> DHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- >>> iN3QnvFqxQQkoPTmztJ >>>> RTNCXTF2dz68TEV0cA&s=yHWSFWSoze0yJhs- >>> YBtijO34uqnnV0LoPfizi0miMNQ&e= >>>> Feedback License: >>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- >>> 2Dopen. >>>> org_who_ipr_feedback- >>> 5Flicense.pdf&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r >>>> =lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- >>> iN3QnvFqxQQkoPTmz >>> tJRTNCXTF2dz68TEV0cA&s=19yavBBd2Ai05CwKnyFOLRNlBnNAtmpKVsTMB6sI >>> TRE&e= >>>> List Guidelines: >>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- >>> 2Dopen. >>>> org_policies-2Dguidelines_mailing- >>> 2Dlists&d=DwIFAg&c=nKjWec2b6R0mOyPaz >>>> 7xtfQ&r=lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- >>> iN3QnvFqxQ >>>> QkoPTmztJRTNCXTF2dz68TEV0cA&s=3bbeWIoIuAK6RwARN2q- >>> t9hPTDAKbwOJ8fMRykpq >>>> ryk&e= >>>> Committee: >>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- >>> 2Dopen. >>> org_committees_virtio_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=lDHJ2F >>> W52oJ >>>> 3lqqsArgFRdcevq01tbLQAw4A_NO7xgI&m=jrQgZ- >>> iN3QnvFqxQQkoPTmztJRTNCXTF2dz >>>> 68TEV0cA&s=U8z-sIxuNy_keXvWYnlIzloNziRKqC1pxOG-x3Hy6SY&e= >>>> Join OASIS: >>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.oasis- >>> 2Dopen. >>> org_join_&d=DwIFAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=lDHJ2FW52oJ3lqqsAr >>> gFRdce >>>> vq01tbLQAw4A_NO7xgI&m=jrQgZ- >>> iN3QnvFqxQQkoPTmztJRTNCXTF2dz68TEV0cA&s=C4 >>>> SQkiR2V1N3I_ri_7fwSiHmcVRNPp2FnVA4gR0-cgM&e= This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. 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* [virtio-comment] Re: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2020-01-23 7:10 ` Jason Wang @ 2020-01-23 7:46 ` Michael S. Tsirkin 2020-01-23 10:00 ` Jason Wang 0 siblings, 1 reply; 11+ messages in thread From: Michael S. Tsirkin @ 2020-01-23 7:46 UTC (permalink / raw) To: Jason Wang; +Cc: Vitaly Mireyno, virtio-comment On Thu, Jan 23, 2020 at 03:10:52PM +0800, Jason Wang wrote: > > On 2020/1/23 下午2:55, Michael S. Tsirkin wrote: > > On Wed, Jan 22, 2020 at 04:06:30PM +0000, Vitaly Mireyno wrote: > > > > > > > -----Original Message----- > > > > From: Michael S. Tsirkin <mst@redhat.com> > > > > Sent: Monday, 20 January, 2020 18:25 > > > > To: Vitaly Mireyno <vmireyno@marvell.com> > > > > Cc: virtio-comment@lists.oasis-open.org; Jason Wang > > > > <jasowang@redhat.com> > > > > Subject: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device > > > > control over the receive buffers length > > > > > > > > External Email > > > > > > > > ---------------------------------------------------------------------- > > > > On Mon, Dec 30, 2019 at 01:59:17PM +0000, Vitaly Mireyno wrote: > > > > > This patch gives devices some level of control over the receive buffers > > > > length. > > > > > The driver declares the minimum receive buffer length, and the device > > > > requests max/min buffer length ratio. > > > > > This is a follow-up to the "[PATCH] virtio-net: Add equal-sized > > > > > receive buffers feature" discussion: > > > > > https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.oasis-2Dope > > > > > n.org_archives_virtio- > > > > 2Dcomment_201912_msg00007.html&d=DwIFAg&c=nKjWec > > > > 2b6R0mOyPaz7xtfQ&r=lDHJ2FW52oJ3lqqsArgFRdcevq01tbLQAw4A_NO7xgI& > > > > m=jrQgZ > > > > > - > > > > iN3QnvFqxQQkoPTmztJRTNCXTF2dz68TEV0cA&s=pDtISMJpw1N9ohot9fluo1N > > > > j1X2s1 > > > > > J_sEVJGg2uwkZk&e= > > > > > > > > > > > > > > > Signed-off-by: Vitaly Mireyno <vmireyno@marvell.com> > > > > > --- > > > > > content.tex | 41 +++++++++++++++++++++++++++++++++++++++-- > > > > > 1 file changed, 39 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/content.tex b/content.tex index d68cfaf..0a4cfba 100644 > > > > > --- a/content.tex > > > > > +++ b/content.tex > > > > > @@ -2815,6 +2815,13 @@ \subsection{Feature bits}\label{sec:Device > > > > > Types / Network Device / Feature bits > > > > \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through > > > > control > > > > > channel. > > > > > > > > > > +\item[VIRTIO_NET_F_RXBUF_LEN_RATIO(57)] Device requests to limit the > > > > > + maximum/minimum receive buffers length ratio. > > > > > + > > > > > +\item[VIRTIO_NET_F_RXBUF_MIN_LEN(58)] Device requests to know the > > > > minimum > > > > > + receive buffers length. Driver declares the minimum receive buffers > > > > > + length. > > > > > + > > > > > \item[VIRTIO_NET_F_GUEST_HDRLEN(59)] Driver can provide the exact > > > > \field{hdr_len} > > > > > value. Device benefits from knowing the exact header length. > > > > > > > > > So I am wondering, when we are switching from regular skbs to XDP, all > > > > buffers become 4K. When we switch back, we get variability again. > > > > All the while some old buffers can be outstanding. > > > > > > > > How will we handle this? > > > > > > > The feature limits the flexibility of the driver to set the descriptors length. > > > It doesn't limit the actual buffer allocation size. So if XDP requires a larger headroom, I don't see a problem. Please excuse my ignorance, but what do you mean by "all buffers become 4K"? > > So linux can switch between skb and XDP mode. In skb mode buffer size > > varies, it works by merging multiple buffers. In XDP a single buffer > > is made big enough to hold the whole packet. Length is fixed. > > > > If we are in XDP mode but buffer was added while in skb mode, > > or vice versa, we recover generally by copying data to > > the correct buffer. This is a temporary slowdown - > > better than dropping packets. > > > > So let's assume the device ratio is 1. > > I guess while in XDP mode, we'll write XDP buffer length into > > this field. But in skb mode, we can make the buffer smaller. > > This implies driver needs to change the min_rx_buf_len? > > > I'm not sure I get here. The header room should be invisible from device > point of view I think. > > Thanks > In fact I am confused. We have this comment: /* This happens when rx buffer size is underestimated * or headroom is not enough because of the buffer * was refilled before XDP is set. This should only * happen for the first several packets, so we don't * care much about its performance. */ but what does ensure that num_buf == 1 except for the first several packets? We seem to be calling add_recvbuf_mergeable which in turn uses ewma to estimate the packet size, but it seems that XDP never updates ewma so the size will be whatever it happened to be, no? I guess we need a counter in this slow path so we can notice it happening ... > > > > > > > > > > > @@ -2861,8 +2868,8 @@ \subsubsection{Legacy Interface: Feature > > > > > bits}\label{sec:Device Types / Network \subsection{Device > > > > > configuration layout}\label{sec:Device Types / Network Device / Device > > > > > configuration layout} \label{sec:Device Types / Block Device / > > > > > Feature bits / Device configuration layout} > > > > > > > > > > -Three driver-read-only configuration fields are currently defined. > > > > > The \field{mac} address field -always exists (though is only valid if > > > > > VIRTIO_NET_F_MAC is set), and > > > > > +The driver-read-only \field{mac} address field always exists (though > > > > > +is only valid if VIRTIO_NET_F_MAC is set), and > > > > > \field{status} only exists if VIRTIO_NET_F_STATUS is set. Two > > > > > read-only bits (for the driver) are currently defined for the status field: > > > > > VIRTIO_NET_S_LINK_UP and VIRTIO_NET_S_ANNOUNCE. > > > > > @@ -2882,12 +2889,22 @@ \subsection{Device configuration > > > > > layout}\label{sec:Device Types / Network Device VIRTIO_NET_F_MTU is > > > > > set. This field specifies the maximum MTU for the driver to use. > > > > > > > > > > +The device-read-only field \field{min_rx_buf_len} only exists if > > > > > +VIRTIO_NET_F_RXBUF_MIN_LEN is set. This field specifies the minimum > > > > > +receive buffers length. > > > > > + > > > > > +The driver-read-only field \field{rx_buf_len_ratio} only exists if > > > > > +VIRTIO_NET_F_RXBUF_LEN_RATIO is set. This field specifies the > > > > > +maximum/minimum receive buffers length ratio. > > > > > + > > Config space access is from point of view of driver (it's part of device > > so it does not make sense to talk about device reading it). > > The point is driver is not supposed to read it, right? > > So s/device-read-only/driver-write-only/ or better "write-only for > > driver". > > > > > > > \begin{lstlisting} > > > > > struct virtio_net_config { > > > > > u8 mac[6]; > > > > > le16 status; > > > > > le16 max_virtqueue_pairs; > > > > > le16 mtu; > > > > > + le32 min_rx_buf_len; > > > > > + le16 rx_buf_len_ratio; > > > > > }; > > > > > \end{lstlisting} > > > > > > > > > > @@ -2916,6 +2933,15 @@ \subsection{Device configuration > > > > > layout}\label{sec:Device Types / Network Device If the driver > > > > > negotiates the VIRTIO_NET_F_STANDBY feature, the device MAY act as a > > > > standby device for a primary device with the same MAC address. > > > > > +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_MIN_LEN feature if > > > > offered. > > > > > + > > > > > +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the > > > > driver > > > > > +MUST set \field{min_rx_buf_len}. > > > > > + > > > > > +A driver MUST NOT modify \field{min_rx_buf_len} once it has been set. > > > > > + > > > > > +A driver SHOULD accept the VIRTIO_NET_F_RXBUF_LEN_RATIO feature if > > > > offered. > > > > > + > > > > > \drivernormative{\subsubsection}{Device configuration layout}{Device > > > > > Types / Network Device / Device configuration layout} > > > > > > > > > > A driver SHOULD negotiate VIRTIO_NET_F_MAC if the device offers it. > > > > > @@ -3281,6 +3307,17 @@ \subsubsection{Setting Up Receive > > > > > Buffers}\label{sec:Device Types / Network Devi If VIRTIO_NET_F_MQ is > > > > > negotiated, each of receiveq1\ldots receiveqN that will be used SHOULD be > > > > populated with receive buffers. > > > > > +If VIRTIO_NET_F_RXBUF_MIN_LEN feature has been negotiated, the > > > > driver > > > > > +MUST initialize all receive virtqueue descriptors \field{len} field > > > > > +with the value greater than or equal to the value configured in the > > > > > +\field{min_rx_buf_len} device configuration field, and allocate > > > > > +receive buffers accordingly. > > > > > + > > > > > +If VIRTIO_NET_F_RXBUF_LEN_RATIO feature has been negotiated, the > > > > > +driver MUST initialize all receive virtqueue descriptors \field{len} > > > > > +field with the value less than or equal to (\field{min_rx_buf_len} * > > > > > +\field{rx_buf_len_ratio}), and allocate receive buffers accordingly. > > > > > + > > > > > \devicenormative{\paragraph}{Setting Up Receive Buffers}{Device Types > > > > > / Network Device / Device Operation / Setting Up Receive Buffers} > > > > > > > > > > The device MUST set \field{num_buffers} to the number of descriptors > > > > > used to > > > > > -- > > > > > > > > > > This publicly archived list offers a means to provide input to the > > > > > OASIS 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In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/ ^ permalink raw reply [flat|nested] 11+ messages in thread
* [virtio-comment] Re: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2020-01-23 7:46 ` Michael S. Tsirkin @ 2020-01-23 10:00 ` Jason Wang 2020-01-23 12:08 ` Michael S. Tsirkin 0 siblings, 1 reply; 11+ messages in thread From: Jason Wang @ 2020-01-23 10:00 UTC (permalink / raw) To: Michael S. Tsirkin; +Cc: Vitaly Mireyno, virtio-comment On 2020/1/23 下午3:46, Michael S. Tsirkin wrote: >>> So linux can switch between skb and XDP mode. In skb mode buffer size >>> varies, it works by merging multiple buffers. In XDP a single buffer >>> is made big enough to hold the whole packet. Length is fixed. >>> >>> If we are in XDP mode but buffer was added while in skb mode, >>> or vice versa, we recover generally by copying data to >>> the correct buffer. This is a temporary slowdown - >>> better than dropping packets. >>> >>> So let's assume the device ratio is 1. >>> I guess while in XDP mode, we'll write XDP buffer length into >>> this field. But in skb mode, we can make the buffer smaller. >>> This implies driver needs to change the min_rx_buf_len? >> I'm not sure I get here. The header room should be invisible from device >> point of view I think. >> >> Thanks >> > In fact I am confused. We have this comment: > > /* This happens when rx buffer size is underestimated > * or headroom is not enough because of the buffer > * was refilled before XDP is set. This should only > * happen for the first several packets, so we don't > * care much about its performance. > */ > > but what does ensure that num_buf == 1 except for the first several > packets? We disable GUEST_TSO, GUEST_UFO, for XDP and the minimal packet is 1500. So it should be fine unless guest MTU is greater than 1500. If guest MTU is greater than 1500 it could be a problem which needs to be fixed. > > We seem to be calling add_recvbuf_mergeable which in turn uses ewma > to estimate the packet size, but it seems that XDP never updates ewma so > the size will be whatever it happened to be, no? It looks to me we can't use EWMA which may cause packet size under estimation. Sticking to MTU should be fine. > > I guess we need a counter in this slow path so we can notice it > happening ... Right, this could be added. Thanks This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/ ^ permalink raw reply [flat|nested] 11+ messages in thread
* [virtio-comment] Re: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length 2020-01-23 10:00 ` Jason Wang @ 2020-01-23 12:08 ` Michael S. Tsirkin 0 siblings, 0 replies; 11+ messages in thread From: Michael S. Tsirkin @ 2020-01-23 12:08 UTC (permalink / raw) To: Jason Wang; +Cc: Vitaly Mireyno, virtio-comment On Thu, Jan 23, 2020 at 06:00:30PM +0800, Jason Wang wrote: > > On 2020/1/23 下午3:46, Michael S. Tsirkin wrote: > > > > So linux can switch between skb and XDP mode. In skb mode buffer size > > > > varies, it works by merging multiple buffers. In XDP a single buffer > > > > is made big enough to hold the whole packet. Length is fixed. > > > > > > > > If we are in XDP mode but buffer was added while in skb mode, > > > > or vice versa, we recover generally by copying data to > > > > the correct buffer. This is a temporary slowdown - > > > > better than dropping packets. > > > > > > > > So let's assume the device ratio is 1. > > > > I guess while in XDP mode, we'll write XDP buffer length into > > > > this field. But in skb mode, we can make the buffer smaller. > > > > This implies driver needs to change the min_rx_buf_len? > > > I'm not sure I get here. The header room should be invisible from device > > > point of view I think. > > > > > > Thanks > > > > > In fact I am confused. We have this comment: > > > > /* This happens when rx buffer size is underestimated > > * or headroom is not enough because of the buffer > > * was refilled before XDP is set. This should only > > * happen for the first several packets, so we don't > > * care much about its performance. > > */ > > > > but what does ensure that num_buf == 1 except for the first several > > packets? > > > We disable GUEST_TSO, GUEST_UFO, for XDP and the minimal packet is 1500. did you mean minimal buffer? that's the part I don't see. what sets buffer size to 1500? > So > it should be fine unless guest MTU is greater than 1500. > > If guest MTU is greater than 1500 it could be a problem which needs to be > fixed. > > > > > > We seem to be calling add_recvbuf_mergeable which in turn uses ewma > > to estimate the packet size, but it seems that XDP never updates ewma so > > the size will be whatever it happened to be, no? > > > It looks to me we can't use EWMA which may cause packet size under > estimation. Sticking to MTU should be fine. > So I'm not seeing things, it's a bug right? > > > > I guess we need a counter in this slow path so we can notice it > > happening ... > > > Right, this could be added. > > Thanks This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. In order to verify user consent to the Feedback License terms and to minimize spam in the list archive, subscription is required before posting. Subscribe: virtio-comment-subscribe@lists.oasis-open.org Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org List help: virtio-comment-help@lists.oasis-open.org List archive: https://lists.oasis-open.org/archives/virtio-comment/ Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists Committee: https://www.oasis-open.org/committees/virtio/ Join OASIS: https://www.oasis-open.org/join/ ^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2020-01-23 12:08 UTC | newest] Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-12-30 13:59 [virtio-comment] [PATCH] virtio-net: Add an optional device control over the receive buffers length Vitaly Mireyno 2020-01-03 15:22 ` Stefan Hajnoczi 2020-01-05 10:28 ` Michael S. Tsirkin 2020-01-05 10:35 ` [virtio-comment] " Michael S. Tsirkin 2020-01-20 16:24 ` [virtio-comment] " Michael S. Tsirkin 2020-01-22 16:06 ` [virtio-comment] RE: [EXT] " Vitaly Mireyno 2020-01-23 6:55 ` [virtio-comment] " Michael S. Tsirkin 2020-01-23 7:10 ` Jason Wang 2020-01-23 7:46 ` Michael S. Tsirkin 2020-01-23 10:00 ` Jason Wang 2020-01-23 12:08 ` Michael S. Tsirkin
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