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| /openbmc/linux/drivers/virtio/ |
| H A D | virtio_ring.c | diff 6c0b057cec5eade4c3afec3908821176931a9997 Wed Mar 29 05:23:00 CDT 2023 Albert Huang <huangjie.albert@bytedance.com> virtio_ring: don't update event idx on get_buf
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>
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