Xuan Zhuo
2023-Mar-29 09:27 UTC
[PATCH v3] virtio_ring: interrupt disable flag updated to vq even with event_triggered is set
On Wed, 29 Mar 2023 15:28:41 +0800, Albert Huang <huangjie.albert at bytedance.com> wrote:> From: "huangjie.albert" <huangjie.albert at 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 at bytedance.com> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > Signed-off-by: Jason Wang <jasowang at 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.> 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 >