KVM: optimize ISR lookups

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We perform ISR lookups twice: during interrupt
injection and on EOI. Typical workloads only have
a single bit set there. So we can avoid ISR scans by
1. counting bits as we set/clear them in ISR
2. on set, caching the injected vector number
3. on clear, invalidating the cache

The real purpose of this is enabling PV EOI
which needs to quickly validate the vector.
But non PV guests also benefit: with this patch,
and without interrupt nesting, apic_find_highest_isr
will always return immediately without scanning ISR.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

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Michael S. Tsirkin 2012-06-24 19:24:26 +03:00 • committed by Avi Kivity

parent 5eadf916df

commit 8680b94b0e

2 changed files with 55 additions and 2 deletions

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53

arch/x86/kvm/lapic.c

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4

arch/x86/kvm/lapic.h

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