From: Xuan Zhuo <xuanzhuo@linux.alibaba.com> To: "Michael S. Tsirkin" <mst@redhat.com> Cc: Willem de Bruijn <willemb@google.com>, netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, Jakub Kicinski <kuba@kernel.org>, Wei Wang <weiwan@google.com>, David Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 3/4] virtio: fix up virtio_disable_cb Date: Thu, 30 Mar 2023 14:54:21 +0800 [thread overview] Message-ID: <1680159261.1588428-1-xuanzhuo@linux.alibaba.com> (raw) In-Reply-To: <20230330024220-mutt-send-email-mst@kernel.org> On Thu, 30 Mar 2023 02:44:44 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote: > On Thu, Mar 30, 2023 at 02:07:37PM +0800, Xuan Zhuo wrote: > > On Wed, 26 May 2021 04:24:40 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote: > > > virtio_disable_cb is currently a nop for split ring with event index. > > > This is because it used to be always called from a callback when we know > > > device won't trigger more events until we update the index. However, > > > now that we run with interrupts enabled a lot we also poll without a > > > callback so that is different: disabling callbacks will help reduce the > > > number of spurious interrupts. > > > Further, if using event index with a packed ring, and if being called > > > from a callback, we actually do disable interrupts which is unnecessary. > > > > > > Fix both issues by tracking whenever we get a callback. If that is > > > the case disabling interrupts with event index can be a nop. > > > If not the case disable interrupts. Note: with a split ring > > > there's no explicit "no interrupts" value. For now we write > > > a fixed value so our chance of triggering an interupt > > > is 1/ring size. It's probably better to write something > > > related to the last used index there to reduce the chance > > > even further. For now I'm keeping it simple. > > > > > > Don't understand, is this patch necessary? For this patch set, we can do without > > this patch. > > > > So doest this patch optimize virtqueue_disable_cb() by reducing a modification of > > vring_used_event(&vq-> split.vring)? > > > > Or I miss something. > > > > Thanks. > > Before this patch virtqueue_disable_cb did nothing at all > for the common case of event index enabled, so > calling it from virtio net would not help matters. I agree with these codes: - if (!vq->event) + if (vq->event) + /* TODO: this is a hack. Figure out a cleaner value to write. */ + vring_used_event(&vq->split.vring) = 0x0; + else I just don't understand event_triggered. > > But the patch is from 2021, isn't it a bit too late to argue? > If you have a cleanup or an optimization in mind, please > post a patch. Sorry, I just have some problems, I don't oppose it. At least it can reduce the modification of vring_used_event(&vq->split.vring). I think it is also beneficial. Thanks very much. > > > > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > > --- > > > drivers/virtio/virtio_ring.c | 26 +++++++++++++++++++++++++- > > > 1 file changed, 25 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > index 71e16b53e9c1..88f0b16b11b8 100644 > > > --- a/drivers/virtio/virtio_ring.c > > > +++ b/drivers/virtio/virtio_ring.c > > > @@ -113,6 +113,9 @@ struct vring_virtqueue { > > > /* Last used index we've seen. */ > > > u16 last_used_idx; > > > > > > + /* Hint for event idx: already triggered no need to disable. */ > > > + bool event_triggered; > > > + > > > union { > > > /* Available for split ring */ > > > struct { > > > @@ -739,7 +742,10 @@ static void virtqueue_disable_cb_split(struct virtqueue *_vq) > > > > > > if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) { > > > vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; > > > - if (!vq->event) > > > + if (vq->event) > > > + /* TODO: this is a hack. Figure out a cleaner value to write. */ > > > + vring_used_event(&vq->split.vring) = 0x0; > > > + else > > > vq->split.vring.avail->flags = > > > cpu_to_virtio16(_vq->vdev, > > > vq->split.avail_flags_shadow); > > > @@ -1605,6 +1611,7 @@ static struct virtqueue *vring_create_virtqueue_packed( > > > vq->weak_barriers = weak_barriers; > > > vq->broken = false; > > > vq->last_used_idx = 0; > > > + vq->event_triggered = false; > > > vq->num_added = 0; > > > vq->packed_ring = true; > > > vq->use_dma_api = vring_use_dma_api(vdev); > > > @@ -1919,6 +1926,12 @@ void virtqueue_disable_cb(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > + /* If device triggered an event already it won't trigger one again: > > > + * no need to disable. > > > + */ > > > + if (vq->event_triggered) > > > + return; > > > + > > > if (vq->packed_ring) > > > virtqueue_disable_cb_packed(_vq); > > > else > > > @@ -1942,6 +1955,9 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > + if (vq->event_triggered) > > > + vq->event_triggered = false; > > > + > > > return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(_vq) : > > > virtqueue_enable_cb_prepare_split(_vq); > > > } > > > @@ -2005,6 +2021,9 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > + if (vq->event_triggered) > > > + vq->event_triggered = false; > > > + > > > return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(_vq) : > > > virtqueue_enable_cb_delayed_split(_vq); > > > } > > > @@ -2044,6 +2063,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq) > > > if (unlikely(vq->broken)) > > > return IRQ_HANDLED; > > > > > > + /* Just a hint for performance: so it's ok that this can be racy! */ > > > + if (vq->event) > > > + vq->event_triggered = true; > > > + > > > pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); > > > if (vq->vq.callback) > > > vq->vq.callback(&vq->vq); > > > @@ -2083,6 +2106,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index, > > > vq->weak_barriers = weak_barriers; > > > vq->broken = false; > > > vq->last_used_idx = 0; > > > + vq->event_triggered = false; > > > vq->num_added = 0; > > > vq->use_dma_api = vring_use_dma_api(vdev); > > > #ifdef DEBUG > > > -- > > > MST > > > > > > _______________________________________________ > > > Virtualization mailing list > > > Virtualization@lists.linux-foundation.org > > > https://lists.linuxfoundation.org/mailman/listinfo/virtualization >
WARNING: multiple messages have this Message-ID (diff)
From: Xuan Zhuo <xuanzhuo@linux.alibaba.com> To: "Michael S. Tsirkin" <mst@redhat.com> Cc: Willem de Bruijn <willemb@google.com>, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Jakub Kicinski <kuba@kernel.org>, Wei Wang <weiwan@google.com>, David Miller <davem@davemloft.net> Subject: Re: [PATCH v3 3/4] virtio: fix up virtio_disable_cb Date: Thu, 30 Mar 2023 14:54:21 +0800 [thread overview] Message-ID: <1680159261.1588428-1-xuanzhuo@linux.alibaba.com> (raw) In-Reply-To: <20230330024220-mutt-send-email-mst@kernel.org> On Thu, 30 Mar 2023 02:44:44 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote: > On Thu, Mar 30, 2023 at 02:07:37PM +0800, Xuan Zhuo wrote: > > On Wed, 26 May 2021 04:24:40 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote: > > > virtio_disable_cb is currently a nop for split ring with event index. > > > This is because it used to be always called from a callback when we know > > > device won't trigger more events until we update the index. However, > > > now that we run with interrupts enabled a lot we also poll without a > > > callback so that is different: disabling callbacks will help reduce the > > > number of spurious interrupts. > > > Further, if using event index with a packed ring, and if being called > > > from a callback, we actually do disable interrupts which is unnecessary. > > > > > > Fix both issues by tracking whenever we get a callback. If that is > > > the case disabling interrupts with event index can be a nop. > > > If not the case disable interrupts. Note: with a split ring > > > there's no explicit "no interrupts" value. For now we write > > > a fixed value so our chance of triggering an interupt > > > is 1/ring size. It's probably better to write something > > > related to the last used index there to reduce the chance > > > even further. For now I'm keeping it simple. > > > > > > Don't understand, is this patch necessary? For this patch set, we can do without > > this patch. > > > > So doest this patch optimize virtqueue_disable_cb() by reducing a modification of > > vring_used_event(&vq-> split.vring)? > > > > Or I miss something. > > > > Thanks. > > Before this patch virtqueue_disable_cb did nothing at all > for the common case of event index enabled, so > calling it from virtio net would not help matters. I agree with these codes: - if (!vq->event) + if (vq->event) + /* TODO: this is a hack. Figure out a cleaner value to write. */ + vring_used_event(&vq->split.vring) = 0x0; + else I just don't understand event_triggered. > > But the patch is from 2021, isn't it a bit too late to argue? > If you have a cleanup or an optimization in mind, please > post a patch. Sorry, I just have some problems, I don't oppose it. At least it can reduce the modification of vring_used_event(&vq->split.vring). I think it is also beneficial. Thanks very much. > > > > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > > --- > > > drivers/virtio/virtio_ring.c | 26 +++++++++++++++++++++++++- > > > 1 file changed, 25 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > index 71e16b53e9c1..88f0b16b11b8 100644 > > > --- a/drivers/virtio/virtio_ring.c > > > +++ b/drivers/virtio/virtio_ring.c > > > @@ -113,6 +113,9 @@ struct vring_virtqueue { > > > /* Last used index we've seen. */ > > > u16 last_used_idx; > > > > > > + /* Hint for event idx: already triggered no need to disable. */ > > > + bool event_triggered; > > > + > > > union { > > > /* Available for split ring */ > > > struct { > > > @@ -739,7 +742,10 @@ static void virtqueue_disable_cb_split(struct virtqueue *_vq) > > > > > > if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) { > > > vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT; > > > - if (!vq->event) > > > + if (vq->event) > > > + /* TODO: this is a hack. Figure out a cleaner value to write. */ > > > + vring_used_event(&vq->split.vring) = 0x0; > > > + else > > > vq->split.vring.avail->flags = > > > cpu_to_virtio16(_vq->vdev, > > > vq->split.avail_flags_shadow); > > > @@ -1605,6 +1611,7 @@ static struct virtqueue *vring_create_virtqueue_packed( > > > vq->weak_barriers = weak_barriers; > > > vq->broken = false; > > > vq->last_used_idx = 0; > > > + vq->event_triggered = false; > > > vq->num_added = 0; > > > vq->packed_ring = true; > > > vq->use_dma_api = vring_use_dma_api(vdev); > > > @@ -1919,6 +1926,12 @@ void virtqueue_disable_cb(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > + /* If device triggered an event already it won't trigger one again: > > > + * no need to disable. > > > + */ > > > + if (vq->event_triggered) > > > + return; > > > + > > > if (vq->packed_ring) > > > virtqueue_disable_cb_packed(_vq); > > > else > > > @@ -1942,6 +1955,9 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > + if (vq->event_triggered) > > > + vq->event_triggered = false; > > > + > > > return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(_vq) : > > > virtqueue_enable_cb_prepare_split(_vq); > > > } > > > @@ -2005,6 +2021,9 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) > > > { > > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > > > + if (vq->event_triggered) > > > + vq->event_triggered = false; > > > + > > > return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(_vq) : > > > virtqueue_enable_cb_delayed_split(_vq); > > > } > > > @@ -2044,6 +2063,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq) > > > if (unlikely(vq->broken)) > > > return IRQ_HANDLED; > > > > > > + /* Just a hint for performance: so it's ok that this can be racy! */ > > > + if (vq->event) > > > + vq->event_triggered = true; > > > + > > > pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); > > > if (vq->vq.callback) > > > vq->vq.callback(&vq->vq); > > > @@ -2083,6 +2106,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index, > > > vq->weak_barriers = weak_barriers; > > > vq->broken = false; > > > vq->last_used_idx = 0; > > > + vq->event_triggered = false; > > > vq->num_added = 0; > > > vq->use_dma_api = vring_use_dma_api(vdev); > > > #ifdef DEBUG > > > -- > > > MST > > > > > > _______________________________________________ > > > Virtualization mailing list > > > Virtualization@lists.linux-foundation.org > > > https://lists.linuxfoundation.org/mailman/listinfo/virtualization > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
next prev parent reply other threads:[~2023-03-30 6:59 UTC|newest] Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-26 8:24 [PATCH v3 0/4] virtio net: spurious interrupt related fixes Michael S. Tsirkin 2021-05-26 8:24 ` Michael S. Tsirkin 2021-05-26 8:24 ` [PATCH v3 1/4] virtio_net: move tx vq operation under tx queue lock Michael S. Tsirkin 2021-05-26 8:24 ` Michael S. Tsirkin 2021-05-27 3:41 ` Jason Wang 2021-05-27 3:41 ` Jason Wang 2021-05-28 22:25 ` Willem de Bruijn 2021-05-28 22:25 ` Willem de Bruijn 2021-06-09 22:03 ` Michael S. Tsirkin 2021-06-09 22:03 ` Michael S. Tsirkin 2021-05-26 8:24 ` [PATCH v3 2/4] virtio_net: move txq wakeups under tx q lock Michael S. Tsirkin 2021-05-26 8:24 ` Michael S. Tsirkin 2021-05-27 3:48 ` Jason Wang 2021-05-27 3:48 ` Jason Wang 2021-05-26 8:24 ` [PATCH v3 3/4] virtio: fix up virtio_disable_cb Michael S. Tsirkin 2021-05-26 8:24 ` Michael S. Tsirkin 2021-05-27 4:01 ` Jason Wang 2021-05-27 4:01 ` Jason Wang 2023-03-30 6:07 ` Xuan Zhuo 2023-03-30 6:07 ` Xuan Zhuo 2023-03-30 6:44 ` Michael S. Tsirkin 2023-03-30 6:44 ` Michael S. Tsirkin 2023-03-30 6:54 ` Xuan Zhuo [this message] 2023-03-30 6:54 ` Xuan Zhuo 2023-03-30 14:04 ` Michael S. Tsirkin 2023-03-30 14:04 ` Michael S. Tsirkin 2023-03-31 3:38 ` Xuan Zhuo 2023-03-31 3:38 ` Xuan Zhuo 2021-05-26 8:24 ` [PATCH v3 4/4] virtio_net: disable cb aggressively Michael S. Tsirkin 2021-05-26 8:24 ` Michael S. Tsirkin 2021-05-26 15:15 ` Eric Dumazet 2021-05-26 15:15 ` Eric Dumazet 2021-05-26 21:22 ` Willem de Bruijn 2021-05-26 21:22 ` Willem de Bruijn 2021-05-26 19:39 ` Jakub Kicinski 2021-05-27 4:09 ` Jason Wang 2021-05-27 4:09 ` Jason Wang 2023-01-16 13:41 ` Laurent Vivier 2023-01-16 13:41 ` Laurent Vivier 2023-01-17 3:48 ` Jason Wang 2023-01-17 3:48 ` Jason Wang 2021-05-26 15:34 ` [PATCH v3 0/4] virtio net: spurious interrupt related fixes Willem de Bruijn 2021-05-26 15:34 ` Willem de Bruijn 2021-06-01 2:53 ` Willem de Bruijn 2021-06-01 2:53 ` Willem de Bruijn 2021-06-09 21:36 ` Willem de Bruijn 2021-06-09 21:36 ` Willem de Bruijn 2021-06-09 22:59 ` Willem de Bruijn 2021-06-09 22:59 ` Willem de Bruijn
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