From: Krishna Kumar2 <krkumar2@in.ibm.com> To: "Michael S. Tsirkin" <mst@redhat.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com>, Carsten Otte <cotte@de.ibm.com>, habanero@linux.vnet.ibm.com, Heiko Carstens <heiko.carstens@de.ibm.com>, kvm@vger.kernel.org, lguest@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux390@de.ibm.com, netdev@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>, Martin Schwidefsky <schwidefsky@de.ibm.com>, steved@us.ibm.com, Tom Lendacky <tahm@linux.vnet.ibm.com>, virtualization@lists.linux-foundation.org, Shirley Ma <xma@us.ibm.com> Subject: Re: [PATCHv2 10/14] virtio_net: limit xmit polling Date: Tue, 24 May 2011 18:20:35 +0530 [thread overview] Message-ID: <OF2D4A7890.FFA91132-ON6525789A.0043E0AC-6525789A.00464690@in.ibm.com> (raw) In-Reply-To: <20110524112901.GB17087@redhat.com> "Michael S. Tsirkin" <mst@redhat.com> wrote on 05/24/2011 04:59:39 PM: > > > > Maybe Rusty means it is a simpler model to free the amount > > > > of space that this xmit needs. We will still fail anyway > > > > at some time but it is unlikely, since earlier iteration > > > > freed up atleast the space that it was going to use. > > > > > > Not sure I nderstand. We can't know space is freed in the previous > > > iteration as buffers might not have been used by then. > > > > Yes, the first few iterations may not have freed up space, but > > later ones should. The amount of free space should increase > > from then on, especially since we try to free double of what > > we consume. > > Hmm. This is only an upper limit on the # of entries in the queue. > Assume that vq size is 4 and we transmit 4 enties without > getting anything in the used ring. The next transmit will fail. > > So I don't really see why it's unlikely that we reach the packet > drop code with your patch. I was assuming 256 entries :) I will try to get some numbers to see how often it is true tomorrow. > > I am not sure of why it was changed, since returning TX_BUSY > > seems more efficient IMHO. > > qdisc_restart() handles requeue'd > > packets much better than a stopped queue, as a significant > > part of this code is skipped if gso_skb is present > > I think this is the argument: > http://www.mail-archive.com/virtualization@lists.linux- > foundation.org/msg06364.html Thanks for digging up that thread! Yes, that one skb would get sent first ahead of possibly higher priority skbs. However, from a performance point, TX_BUSY code skips a lot of checks and code for all subsequent packets till the device is restarted. I can test performance with both cases and report what I find (the requeue code has become very simple and clean from "horribly complex", thanks to Herbert and Dave). > > (qdisc > > will eventually start dropping packets when tx_queue_len is > > tx_queue_len is a pretty large buffer so maybe no. I remember seeing tons of drops (pfifo_fast_enqueue) when xmit returns TX_BUSY. > I think the packet drops from the scheduler queue can also be > done intelligently (e.g. with CHOKe) which should > work better than dropping a random packet? I am not sure of that - choke_enqueue checks against a random skb to drop current skb, and also during congestion. But for my "sample driver xmit", returning TX_BUSY could still allow to be used with CHOKe. thanks, - KK
WARNING: multiple messages have this Message-ID (diff)
From: Krishna Kumar2 <krkumar2-xthvdsQ13ZrQT0dZR+AlfA@public.gmane.org> To: "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Cc: habanero-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org, lguest-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, Shirley Ma <xma-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>, kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Carsten Otte <cotte-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, linux-s390-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, steved-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org, Christian Borntraeger <borntraeger-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, Tom Lendacky <tahm-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Martin Schwidefsky <schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, linux390-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org Subject: Re: [PATCHv2 10/14] virtio_net: limit xmit polling Date: Tue, 24 May 2011 18:20:35 +0530 [thread overview] Message-ID: <OF2D4A7890.FFA91132-ON6525789A.0043E0AC-6525789A.00464690@in.ibm.com> (raw) In-Reply-To: <20110524112901.GB17087-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> "Michael S. Tsirkin" <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote on 05/24/2011 04:59:39 PM: > > > > Maybe Rusty means it is a simpler model to free the amount > > > > of space that this xmit needs. We will still fail anyway > > > > at some time but it is unlikely, since earlier iteration > > > > freed up atleast the space that it was going to use. > > > > > > Not sure I nderstand. We can't know space is freed in the previous > > > iteration as buffers might not have been used by then. > > > > Yes, the first few iterations may not have freed up space, but > > later ones should. The amount of free space should increase > > from then on, especially since we try to free double of what > > we consume. > > Hmm. This is only an upper limit on the # of entries in the queue. > Assume that vq size is 4 and we transmit 4 enties without > getting anything in the used ring. The next transmit will fail. > > So I don't really see why it's unlikely that we reach the packet > drop code with your patch. I was assuming 256 entries :) I will try to get some numbers to see how often it is true tomorrow. > > I am not sure of why it was changed, since returning TX_BUSY > > seems more efficient IMHO. > > qdisc_restart() handles requeue'd > > packets much better than a stopped queue, as a significant > > part of this code is skipped if gso_skb is present > > I think this is the argument: > http://www.mail-archive.com/virtualization-cunTk1MwBs/ROKNJybVBZg@public.gmane.org > foundation.org/msg06364.html Thanks for digging up that thread! Yes, that one skb would get sent first ahead of possibly higher priority skbs. However, from a performance point, TX_BUSY code skips a lot of checks and code for all subsequent packets till the device is restarted. I can test performance with both cases and report what I find (the requeue code has become very simple and clean from "horribly complex", thanks to Herbert and Dave). > > (qdisc > > will eventually start dropping packets when tx_queue_len is > > tx_queue_len is a pretty large buffer so maybe no. I remember seeing tons of drops (pfifo_fast_enqueue) when xmit returns TX_BUSY. > I think the packet drops from the scheduler queue can also be > done intelligently (e.g. with CHOKe) which should > work better than dropping a random packet? I am not sure of that - choke_enqueue checks against a random skb to drop current skb, and also during congestion. But for my "sample driver xmit", returning TX_BUSY could still allow to be used with CHOKe. thanks, - KK
next prev parent reply other threads:[~2011-05-24 12:48 UTC|newest] Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-05-19 23:10 [PATCHv2 00/14] virtio and vhost-net performance enhancements Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:10 ` [PATCHv2 01/14] virtio: event index interface Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-21 2:29 ` Rusty Russell 2011-05-21 2:29 ` Rusty Russell 2011-05-21 2:29 ` Rusty Russell 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:10 ` [PATCHv2 02/14] virtio ring: inline function to check for events Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-21 2:29 ` Rusty Russell 2011-05-21 2:29 ` Rusty Russell 2011-05-21 2:29 ` Rusty Russell 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:10 ` [PATCHv2 03/14] virtio_ring: support event idx feature Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-21 2:31 ` Rusty Russell 2011-05-21 2:31 ` Rusty Russell 2011-05-21 2:31 ` Rusty Russell 2011-05-19 23:10 ` [PATCHv2 04/14] vhost: support event index Michael S. Tsirkin 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-21 2:31 ` Rusty Russell 2011-05-21 2:31 ` Rusty Russell 2011-05-21 2:31 ` Rusty Russell 2011-05-19 23:10 ` Michael S. Tsirkin 2011-05-19 23:11 ` [PATCHv2 05/14] virtio_test: " Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-21 2:32 ` Rusty Russell 2011-05-21 2:32 ` Rusty Russell 2011-05-21 2:32 ` Rusty Russell 2011-05-19 23:11 ` [PATCHv2 06/14] virtio: add api for delayed callbacks Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-21 2:33 ` Rusty Russell 2011-05-21 2:33 ` Rusty Russell 2011-05-21 2:33 ` Rusty Russell 2011-05-19 23:11 ` [PATCHv2 07/14] virtio_net: delay TX callbacks Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` [PATCHv2 08/14] virtio_ring: Add capacity check API Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` [PATCHv2 09/14] virtio_net: fix TX capacity checks using new API Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-21 2:13 ` Rusty Russell 2011-05-21 2:13 ` Rusty Russell 2011-05-21 2:13 ` Rusty Russell 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:11 ` [PATCHv2 10/14] virtio_net: limit xmit polling Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-21 2:19 ` Rusty Russell 2011-05-21 2:19 ` Rusty Russell 2011-05-21 2:19 ` Rusty Russell 2011-05-22 12:10 ` Michael S. Tsirkin 2011-05-22 12:10 ` Michael S. Tsirkin 2011-05-23 2:07 ` Rusty Russell 2011-05-23 2:07 ` Rusty Russell 2011-05-23 11:19 ` Michael S. Tsirkin 2011-05-23 11:19 ` Michael S. Tsirkin 2011-05-23 11:19 ` Michael S. Tsirkin 2011-05-24 7:54 ` Krishna Kumar2 2011-05-24 7:54 ` Krishna Kumar2 2011-05-24 9:12 ` Michael S. Tsirkin 2011-05-24 9:12 ` Michael S. Tsirkin 2011-05-24 9:12 ` Michael S. Tsirkin 2011-05-24 9:27 ` Krishna Kumar2 2011-05-24 9:27 ` Krishna Kumar2 2011-05-24 11:29 ` Michael S. Tsirkin 2011-05-24 11:29 ` Michael S. Tsirkin 2011-05-24 12:50 ` Krishna Kumar2 [this message] 2011-05-24 12:50 ` Krishna Kumar2 2011-05-24 13:52 ` Michael S. Tsirkin 2011-05-24 13:52 ` Michael S. Tsirkin 2011-05-24 13:52 ` Michael S. Tsirkin 2011-05-24 12:50 ` Krishna Kumar2 2011-05-24 11:29 ` Michael S. Tsirkin 2011-05-24 7:54 ` Krishna Kumar2 2011-05-25 1:28 ` Rusty Russell 2011-05-25 1:28 ` Rusty Russell 2011-05-25 5:50 ` Michael S. Tsirkin 2011-05-25 5:50 ` Michael S. Tsirkin 2011-05-25 5:50 ` Michael S. Tsirkin 2011-05-25 1:28 ` Rusty Russell 2011-05-25 1:35 ` Rusty Russell 2011-05-25 1:35 ` Rusty Russell 2011-05-25 1:35 ` Rusty Russell 2011-05-25 6:07 ` Michael S. Tsirkin 2011-05-25 6:07 ` Michael S. Tsirkin 2011-05-26 3:28 ` Rusty Russell 2011-05-26 3:28 ` Rusty Russell 2011-05-26 3:28 ` Rusty Russell 2011-05-28 20:02 ` Michael S. Tsirkin 2011-05-28 20:02 ` Michael S. Tsirkin 2011-05-30 6:27 ` Rusty Russell 2011-05-30 6:27 ` Rusty Russell 2011-05-30 6:27 ` Rusty Russell 2011-05-28 20:02 ` Michael S. Tsirkin 2011-05-25 6:07 ` Michael S. Tsirkin 2011-05-23 2:07 ` Rusty Russell 2011-05-22 12:10 ` Michael S. Tsirkin 2011-05-19 23:11 ` Michael S. Tsirkin 2011-05-19 23:12 ` [PATCHv2 11/14] virtio: don't delay avail index update Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-21 2:26 ` Rusty Russell 2011-05-21 2:26 ` Rusty Russell 2011-05-21 2:26 ` Rusty Russell 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` [PATCHv2 12/14] virtio: 64 bit features Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` [PATCHv2 13/14] virtio_test: update for " Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` [PATCHv2 14/14] vhost: fix " Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:12 ` Michael S. Tsirkin 2011-05-19 23:20 ` [PATCHv2 00/14] virtio and vhost-net performance enhancements David Miller 2011-05-19 23:20 ` David Miller 2011-05-20 7:51 ` Rusty Russell 2011-05-20 7:51 ` Rusty Russell 2011-05-20 7:51 ` Rusty Russell 2011-05-26 15:32 ` [PERF RESULTS] " Krishna Kumar2 2011-05-26 15:32 ` Krishna Kumar2 2011-05-26 15:42 ` Shirley Ma 2011-05-26 16:21 ` Krishna Kumar2 2011-05-26 16:21 ` Krishna Kumar2 [not found] ` <OFF9D0E604.B865A006-ON6525789C.00597010-6525789C.0059987A@LocalDomain> 2011-05-26 16:29 ` Krishna Kumar2 2011-05-26 16:29 ` Krishna Kumar2 2011-05-26 16:29 ` Krishna Kumar2 2011-05-26 15:32 ` Krishna Kumar2
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