Hi geniuses, Please help review this rebased version which enables the guest LBR. We already upstreamed the guest LBR support in the host perf, please check more details in each commit and feel free to test and comment. v13->v13 RESEND Changelog: - Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx> v12->v13 Changelog: - remove perf patches since they're merged already; - add a minor patch to refactor MSR_IA32_DEBUGCTLMSR set/get handler; - add a minor patch to expose vmx_set_intercept_for_msr(); - add a minor patch to adjust features visibility via IA32_PERF_CAPABILITIES; - spilt the big patch to three pieces (0004-0006) for better understanding and review; - make the LBR_FMT exposure patch as the last step to enable guest LBR; Previous: https://lore.kernel.org/kvm/20201030035220.102403-1-like.xu@xxxxxxxxxxxxxxx/ --- The last branch recording (LBR) is a performance monitor unit (PMU) feature on Intel processors that records a running trace of the most recent branches taken by the processor in the LBR stack. This patch series is going to enable this feature for plenty of KVM guests. with this patch set, the following error will be gone forever and cloud developers can better understand their programs with less profiling overhead: $ perf record -b lbr ${WORKLOAD} or $ perf record --call-graph lbr ${WORKLOAD} Error: cycles: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat' The user space could configure whether it's enabled or not for each guest via MSR_IA32_PERF_CAPABILITIES msr. As a first step, a guest could only enable LBR feature if its cpu model is the same as the host since the LBR feature is still one of model specific features. If it's enabled on the guest, the guest LBR driver would accesses the LBR MSR (including IA32_DEBUGCTLMSR and records MSRs) as host does. The first guest access on the LBR related MSRs is always interceptible. The KVM trap would create a special LBR event (called guest LBR event) which enables the callstack mode and none of hardware counter is assigned. The host perf would enable and schedule this event as usual. Guest's first access to a LBR registers gets trapped to KVM, which creates a guest LBR perf event. It's a regular LBR perf event which gets the LBR facility assigned from the perf subsystem. Once that succeeds, the LBR stack msrs are passed through to the guest for efficient accesses. However, if another host LBR event comes in and takes over the LBR facility, the LBR msrs will be made interceptible, and guest following accesses to the LBR msrs will be trapped and meaningless. Because saving/restoring tens of LBR MSRs (e.g. 32 LBR stack entries) in VMX transition brings too excessive overhead to frequent vmx transition itself, the guest LBR event would help save/restore the LBR stack msrs during the context switching with the help of native LBR event callstack mechanism, including LBR_SELECT msr. If the guest no longer accesses the LBR-related MSRs within a scheduling time slice and the LBR enable bit is unset, vPMU would release its guest LBR event as a normal event of a unused vPMC and the pass-through state of the LBR stack msrs would be canceled. --- LBR testcase: echo 1 > /proc/sys/kernel/watchdog echo 25 > /proc/sys/kernel/perf_cpu_time_max_percent echo 5000 > /proc/sys/kernel/perf_event_max_sample_rate echo 0 > /proc/sys/kernel/perf_cpu_time_max_percent ./perf record -b ./br_instr a - Perf report on the host: Samples: 72K of event 'cycles', Event count (approx.): 72512 Overhead Command Source Shared Object Source Symbol Target Symbol Basic Block Cycles 12.12% br_instr br_instr [.] cmp_end [.] lfsr_cond 1 11.05% br_instr br_instr [.] lfsr_cond [.] cmp_end 5 8.81% br_instr br_instr [.] lfsr_cond [.] cmp_end 4 5.04% br_instr br_instr [.] cmp_end [.] lfsr_cond 20 4.92% br_instr br_instr [.] lfsr_cond [.] cmp_end 6 4.88% br_instr br_instr [.] cmp_end [.] lfsr_cond 6 4.58% br_instr br_instr [.] cmp_end [.] lfsr_cond 5 - Perf report on the guest: Samples: 92K of event 'cycles', Event count (approx.): 92544 Overhead Command Source Shared Object Source Symbol Target Symbol Basic Block Cycles 12.03% br_instr br_instr [.] cmp_end [.] lfsr_cond 1 11.09% br_instr br_instr [.] lfsr_cond [.] cmp_end 5 8.57% br_instr br_instr [.] lfsr_cond [.] cmp_end 4 5.08% br_instr br_instr [.] lfsr_cond [.] cmp_end 6 5.06% br_instr br_instr [.] cmp_end [.] lfsr_cond 20 4.87% br_instr br_instr [.] cmp_end [.] lfsr_cond 6 4.70% br_instr br_instr [.] cmp_end [.] lfsr_cond 5 Conclusion: the profiling results on the guest are similar to that on the host. Like Xu (10): KVM: x86: Move common set/get handler of MSR_IA32_DEBUGCTLMSR to VMX KVM: x86/vmx: Make vmx_set_intercept_for_msr() non-static KVM: x86/pmu: Use IA32_PERF_CAPABILITIES to adjust features visibility KVM: vmx/pmu: Clear PMU_CAP_LBR_FMT when guest LBR is disabled KVM: vmx/pmu: Create a guest LBR event when vcpu sets DEBUGCTLMSR_LBR KVM: vmx/pmu: Pass-through LBR msrs when the guest LBR event is ACTIVE KVM: vmx/pmu: Reduce the overhead of LBR pass-through or cancellation KVM: vmx/pmu: Emulate legacy freezing LBRs on virtual PMI KVM: vmx/pmu: Expose LBR_FMT in the MSR_IA32_PERF_CAPABILITIES KVM: vmx/pmu: Release guest LBR event via lazy release mechanism arch/x86/kvm/pmu.c | 12 +- arch/x86/kvm/pmu.h | 5 + arch/x86/kvm/vmx/capabilities.h | 22 ++- arch/x86/kvm/vmx/pmu_intel.c | 292 +++++++++++++++++++++++++++++++- arch/x86/kvm/vmx/vmx.c | 52 +++++- arch/x86/kvm/vmx/vmx.h | 28 +++ arch/x86/kvm/x86.c | 15 +- 7 files changed, 400 insertions(+), 26 deletions(-) -- 2.29.2
