From 6c0b057cec5eade4c3afec3908821176931a9997 Mon Sep 17 00:00:00 2001
From: Albert Huang <huangjie.albert@bytedance.com>
Date: Wed, 29 Mar 2023 18:23:00 +0800
Subject: [PATCH] virtio_ring: don't update event idx on get_buf
Git-commit: 6c0b057cec5eade4c3afec3908821176931a9997
Patch-mainline: v6.4-rc1
References: git-fixes
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>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
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 4c3bb0ddeb9b..34e3849629da 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -854,6 +854,14 @@ 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;
@@ -1699,6 +1707,14 @@ 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);
}
@@ -2330,12 +2346,6 @@ 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
--
2.35.3