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authorAlbert Huang2023-03-29 18:23:00 +0800
committerGreg Kroah-Hartman2023-05-11 23:03:31 +0900
commitce818ee162cf4b528f717bbab089eeb6b54ff428 (patch)
treee9590795ff41965b3a9fc639854ce7dd88b48a34 /drivers/virtio
parent428cc252701d6864151f3a296ffc23e1e49a7408 (diff)
virtio_ring: don't update event idx on get_buf
[ 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>
Diffstat (limited to 'drivers/virtio')
-rw-r--r--drivers/virtio/virtio_ring.c22
1 files changed, 16 insertions, 6 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 2e7689bb933b..90d514c14179 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