On Sat, Jul 10, 2021 at 07:49:14PM -0400, Sasha Levin wrote:
From: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
[ Upstream commit 8d622d21d24803408b256d96463eac4574dcf067 ]
virtio_disable_cb is currently a nop for split ring with event index.
This is because it used to be always called from a callback when we know
device won't trigger more events until we update the index. However,
now that we run with interrupts enabled a lot we also poll without a
callback so that is different: disabling callbacks will help reduce the
number of spurious interrupts.
Further, if using event index with a packed ring, and if being called
from a callback, we actually do disable interrupts which is unnecessary.
Fix both issues by tracking whenever we get a callback. If that is
the case disabling interrupts with event index can be a nop.
If not the case disable interrupts. Note: with a split ring
there's no explicit "no interrupts" value. For now we write
a fixed value so our chance of triggering an interupt
is 1/ring size. It's probably better to write something
related to the last used index there to reduce the chance
even further. For now I'm keeping it simple.
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
I am not sure we want this in stable yet. It should in theory
fix the reported interrupt storms but the reporter is on vacation.