I'm looking at reducing the interrupt overhead for virtualized guests: some workloads spend a large part of their time processing interrupts. This patchset supplies infrastructure to reduce the IRQ ack overhead on x86: the idea is to add an eoi_write callback that we can then optimize without touching other apic functionality. The main user is kvm: on kvm, an EOI write from the guest causes an expensive exit to host; we can avoid this using shared memory as the last patches in the series demonstrate. But I also wrote a micro-optimized version for the regular x2apic: this shaves off a branch and about 9 instructions from EOI when x2apic is used, and a comment in ack_APIC_irq implies that someone counted instructions there, at some point. That's patch 4 in the series - if someone's unhappy with this patch specifically this patch can be dropped as nothing else in the series depends on it. Also included in the patchset are a couple of trivial macro fixes. The patches work fine on my boxes. See individual patches for perf tests. You need to patch qemu to whitelist the kvm feature. qemu patch will be sent as a reply to this mail. The patches are against 3.4-rc7 - let me know if I need to rebase. Please review, and consider for linux 3.5. Thanks, MST Changes from v3: Address review comments by Marcelo: Multiple cosmetic changes eoi -> pv_eoi Added multiple comments Changes from v2: Kill guest with GP on an illegal MSR value Add documentation Changes from v1: Add host side patch to series Remove kvm-specific __test_and_clear_bit, document that x86 one does what we want already Clear msr on cpu unplug Michael S. Tsirkin (5): kvm_para: guest side for eoi avoidance x86/bitops: note on __test_and_clear_bit atomicity kvm: host side for eoi optimization kvm: eoi msi documentation kvm: only sync when attention bits set Documentation/virtual/kvm/msr.txt | 32 +++++++++ arch/x86/include/asm/bitops.h | 13 +++- arch/x86/include/asm/kvm_host.h | 12 +++ arch/x86/include/asm/kvm_para.h | 7 ++ arch/x86/kernel/kvm.c | 51 +++++++++++++- arch/x86/kvm/cpuid.c | 1 + arch/x86/kvm/irq.c | 2 +- arch/x86/kvm/lapic.c | 137 +++++++++++++++++++++++++++++++++++-- arch/x86/kvm/lapic.h | 2 + arch/x86/kvm/trace.h | 34 +++++++++ arch/x86/kvm/x86.c | 8 ++- 11 files changed, 287 insertions(+), 12 deletions(-) -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
