[PATCH 00/10] KVM: x86/pmu: Optimize triggering of emulated events

Sean Christopherson
2023-11-10T02:29:02Z

Optimize code used by, or which impacts, kvm_pmu_trigger_event() to try
and make a dent in the overhead of emulating PMU events in software, which
is quite noticeable due to it kicking in anytime the guest has a vPMU and
KVM is skipping an instruction.

Note, Jim has a proposal/idea[*] (that I supported) to make
kvm_pmu_trigger_event() even more performant. I opted not to do that as
it's a bit more invasive, and I started chewing on this not so much because
I care _that_ much about performance, but because it irritates me that the
PMU code makes things way harder than they need to be.

Note #2, this applies on top of my other two PMU series:

https://lore.kernel.org/all/20231103230541.352265-1-seanjc@google.com
https://lore.kernel.org/all/20231110021306.1269082-1-seanjc@google.com

Those series fix actual functional issues, i.e. I'll definitely apply them
first (there's definitely no rush on this one).

[*] https://lore.kernel.org/all/CALMp9eQGqqo66fQGwFJMc3y+9XdUrL7ageE8kvoAOV6NJGfJpw@mail.gmail.com

Sean Christopherson (10):
KVM: x86/pmu: Zero out PMU metadata on AMD if PMU is disabled
KVM: x86/pmu: Add common define to capture fixed counters offset
KVM: x86/pmu: Move pmc_idx => pmc translation helper to common code
KVM: x86/pmu: Snapshot and clear reprogramming bitmap before
reprogramming
KVM: x86/pmu: Add macros to iterate over all PMCs given a bitmap
KVM: x86/pmu: Process only enabled PMCs when emulating events in
software
KVM: x86/pmu: Snapshot event selectors that KVM emulates in software
KVM: x86/pmu: Expand the comment about what bits are check emulating
events
KVM: x86/pmu: Check eventsel first when emulating (branch) insns
retired
KVM: x86/pmu: Avoid CPL lookup if PMC enabline for USER and KERNEL is
the same

arch/x86/include/asm/kvm-x86-pmu-ops.h | 1 -
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/pmu.c | 143 +++++++++++++++----------
arch/x86/kvm/pmu.h | 52 ++++++++-
arch/x86/kvm/svm/pmu.c | 7 +-
arch/x86/kvm/vmx/nested.c | 2 +-
arch/x86/kvm/vmx/pmu_intel.c | 44 ++------
arch/x86/kvm/x86.c | 6 +-
8 files changed, 154 insertions(+), 102 deletions(-)

base-commit: ef1883475d4a24d8eaebb84175ed46206a688103
--
2.42.0.869.gea05f2083d-goog