From: Albert Huang huangjie.albert@bytedance.com
[ Upstream commit 6c0b057cec5eade4c3afec3908821176931a9997 ]
In virtio_net, if we disable napi_tx, when we trigger a tx interrupt, the vq->event_triggered will be set to true. It is then never reset until we explicitly call virtqueue_enable_cb_delayed or virtqueue_enable_cb_prepare.
If we disable the napi_tx, virtqueue_enable_cb* will only be called when the tx ring is getting relatively empty.
Since event_triggered is true, VRING_AVAIL_F_NO_INTERRUPT or VRING_PACKED_EVENT_FLAG_DISABLE will not be set. As a result we update vring_used_event(&vq->split.vring) or vq->packed.vring.driver->off_wrap every time we call virtqueue_get_buf_ctx. This causes more interrupts.
To summarize: 1) event_triggered was set to true in vring_interrupt() 2) after this nothing will happen in 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 and then it will publish a new event index
To fix: update VRING_AVAIL_F_NO_INTERRUPT or VRING_PACKED_EVENT_FLAG_DISABLE in the vq when we call virtqueue_disable_cb even when event_triggered is true.
Tested with iperf: iperf3 tcp stream: vm1 -----------------> vm2 vm2 just receives tcp data stream from vm1, and sends acks to vm1, there are many tx interrupts in vm2. with the patch applied 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.
v3->v4: -remove change for -"if (vq->packed.event_flags_shadow != VRING_PACKED_EVENT_FLAG_DISABLE)" -in virtqueue_disable_cb_packed
Fixes: 8d622d21d248 ("virtio: fix up virtio_disable_cb") Signed-off-by: Albert Huang huangjie.albert@bytedance.com Signed-off-by: Michael S. Tsirkin mst@redhat.com Signed-off-by: Jason Wang jasowang@redhat.com Message-Id: 20230329102300.61000-1-huangjie.albert@bytedance.com Signed-off-by: Michael S. Tsirkin mst@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/virtio/virtio_ring.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 723c4e29e1d3b..5bee2ab62111b 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -848,6 +848,14 @@ 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; @@ -1687,6 +1695,14 @@ static void virtqueue_disable_cb_packed(struct virtqueue *_vq)
if (vq->packed.event_flags_shadow != VRING_PACKED_EVENT_FLAG_DISABLE) { 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); } @@ -2309,12 +2325,6 @@ 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