Messages in this thread | | | From | 黄杰 <> | Date | Wed, 29 Mar 2023 17:33:23 +0800 | Subject | Re: [External] Re: [PATCH v3] virtio_ring: interrupt disable flag updated to vq even with event_triggered is set |
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Xuan Zhuo <xuanzhuo@linux.alibaba.com> 于2023年3月29日周三 17:27写道: > > On Wed, 29 Mar 2023 15:28:41 +0800, Albert Huang <huangjie.albert@bytedance.com> wrote: > > From: "huangjie.albert" <huangjie.albert@bytedance.com> > > > > in virtio_net, if we disable the napi_tx, when we triger a tx interrupt, > > the vq->event_triggered will be set to true. It will no longer be set to > > false. Unless we explicitly call virtqueue_enable_cb_delayed or > > virtqueue_enable_cb_prepare. > > > > If we disable the napi_tx, it will only be called when the tx ring > > buffer is relatively small. > > > > Because event_triggered is true. Therefore, VRING_AVAIL_F_NO_INTERRUPT or > > VRING_PACKED_EVENT_FLAG_DISABLE will not be set. So we update > > vring_used_event(&vq->split.vring) or vq->packed.vring.driver->off_wrap > > every time we call virtqueue_get_buf_ctx.This bring more interruptions. > > > > To summarize: > > 1) event_triggered was set to true in vring_interrupt() > > 2) after this nothing will happen for virtqueue_disable_cb() so > > VRING_AVAIL_F_NO_INTERRUPT is not set in avail_flags_shadow > > 3) virtqueue_get_buf_ctx_split() will still think the cb is enabled > > then it tries to publish new event > > > > To fix: > > update VRING_AVAIL_F_NO_INTERRUPT or VRING_PACKED_EVENT_FLAG_DISABLE to vq > > when we call virtqueue_disable_cb even the event_triggered is set to true. > > > > Tested with iperf: > > iperf3 tcp stream: > > vm1 -----------------> vm2 > > vm2 just receives tcp data stream from vm1, and sends the ack to vm1, > > there are many tx interrupts in vm2. > > but without event_triggered there are just a few tx interrupts. > > > > v2->v3: > > -update the interrupt disable flag even with the event_triggered is set, > > -instead of checking whether event_triggered is set in > > -virtqueue_get_buf_ctx_{packed/split}, will cause the drivers which have > > -not called virtqueue_{enable/disable}_cb to miss notifications. > > > > Fixes: 8d622d21d248 ("virtio: fix up virtio_disable_cb") > > Signed-off-by: huangjie.albert <huangjie.albert@bytedance.com> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > Signed-off-by: Jason Wang <jasowang@redhat.com> > > --- > > drivers/virtio/virtio_ring.c | 24 +++++++++++++++++------- > > 1 file changed, 17 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > index 307e139cb11d..ad74463a48ee 100644 > > --- a/drivers/virtio/virtio_ring.c > > +++ b/drivers/virtio/virtio_ring.c > > @@ -812,6 +812,14 @@ 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 device triggered an event already it won't trigger one again: > > + * no need to disable. > > + */ > > + if (vq->event_triggered) > > + return; > > + > > if (vq->event) > > /* TODO: this is a hack. Figure out a cleaner value to write. */ > > vring_used_event(&vq->split.vring) = 0x0; > > @@ -1544,8 +1552,16 @@ static void virtqueue_disable_cb_packed(struct virtqueue *_vq) > > { > > struct vring_virtqueue *vq = to_vvq(_vq); > > > > - if (vq->packed.event_flags_shadow != VRING_PACKED_EVENT_FLAG_DISABLE) { > > + if (!(vq->packed.event_flags_shadow & VRING_PACKED_EVENT_FLAG_DISABLE)) { > > This seems to be another problem. > > Thanks. >
Here, we are only making this change to maintain consistency with virtqueue_disable_cb_split. Is there any concern with doing so?
Thanks.
> > > vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE; > > + > > + /* > > + * If device triggered an event already it won't trigger one again: > > + * no need to disable. > > + */ > > + if (vq->event_triggered) > > + return; > > + > > vq->packed.vring.driver->flags = > > cpu_to_le16(vq->packed.event_flags_shadow); > > } > > @@ -2063,12 +2079,6 @@ 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 > > -- > > 2.31.1 > >
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