Re: [PATCH] KVM: Improve interrupt response


* Avi Kivity <avi@xxxxxxxxxxxx> wrote:

From: Dor Laor <dor.laor@xxxxxxxxxxxx>

The current interrupt injection mechanism might delay an interrupt
under the following circumstances:

- if injection fails because the guest is not interruptible (rflags.IF clear,
or after a 'mov ss' or 'sti' instruction). Userspace can check rflags,
but the other cases or not testable under the current API.
- if injection fails because of a fault during delivery. This probably
never happens under normal guests.
- if injection fails due to a physical interrupt causing a vmexit so that
it can be handled by the host.

in all cases the guest proceeds without processing the interrupt,
reducing the interactive feel and interrupt throughput of the guest.

This patch fixes the situation by allowing userspace to request an
exit when the 'interrupt window' opens, so that it can re-inject the
interrupt at the right time. Guest interactivity is very visibly
improved.

Andrew, i'd argue for this to be included in v2.6.20, because it's an
obvious bugfix. I've tested this patch and it's included in current -rt
and i saw no regressions.

Acked-by: Ingo Molnar <mingo@xxxxxxx>

Ingo
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