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vhost_user_backend: call get_used_event from needs_notification

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This change, combined with the compiler hint to inline get_used_event,
shortens the window between the memory read and the actual check by
calling get_used_event from needs_notification.

Without it, when putting enough pressure on the vring, it's possible
that a notification is wrongly omitted, causing the queue to stall.

Signed-off-by: Sergio Lopez <slp@redhat.com>
This commit is contained in:
Sergio Lopez
2020-03-10 05:43:13 -04:00
committed by Rob Bradford
parent 536323d9fb
commit 3957d1ee27
3 changed files with 4 additions and 10 deletions
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3
src/bin/vhost_user_fs.rs
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@@ -126,8 +126,7 @@ impl<F: FileSystem + Send + Sync + 'static> VhostUserFsBackend<F> {
.map_err(Error::ProcessQueue)?;
if self.event_idx {
if let Some(used_idx) = vring.mut_queue().add_used(mem, head_index, 0) {
let used_event = vring.mut_queue().get_used_event(mem);
if vring.needs_notification(Wrapping(used_idx), used_event) {
if vring.needs_notification(&mem, Wrapping(used_idx)) {
vring.signal_used_queue().map_err(Error::SignalQueue)?;
}
used_any = true;