Messages in this thread | | | Subject | Re: [PATCH v13 00/10] Guest Last Branch Recording Enabling (KVM part) | From | "Xu, Like" <> | Date | Fri, 14 Aug 2020 16:48:10 +0800 |
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Are there no interested reviewers or users?
Just a kindly ping.
On 2020/7/26 23:32, Like Xu wrote: > Hi Paolo, > > Please review this new version for the Kernel 5.9 release, and > Sean may not review them as he said in the previous email > https://lore.kernel.org/kvm/20200710162819.GF1749@linux.intel.com/ > > You may cherry-pick the perf patches "3cb9d5464c1c..e1ad1ac2deb8" > from the branch "tip/perf/core" of scm/linux/kernel/git/tip/tip.git > as PeterZ said in the previous email > https://lore.kernel.org/kvm/20200703075646.GJ117543@hirez.programming.kicks-ass.net/ > > We may also apply the qemu-devel patch to the upstream qemu and try > the QEMU command lines with '-cpu host' or '-cpu host,pmu=true,lbr=true'. > > The following error will be gone forever with the patchset: > > $ 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' > > Please check more details in each commit and feel free to test. > > v12->v13 Changelog: > - remove perf patches since they're queued in the tip/perf/core; > - 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 initialize perf_capabilities in the intel_pmu_init(); > - 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/20200613080958.132489-1-like.xu@linux.intel.com/ > > --- > > 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. > > 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 and expose it > KVM: vmx/pmu: Initialize vcpu perf_capabilities once in intel_pmu_init() > 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 to 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 | 296 +++++++++++++++++++++++++++++++- > arch/x86/kvm/vmx/vmx.c | 44 ++++- > arch/x86/kvm/vmx/vmx.h | 28 +++ > arch/x86/kvm/x86.c | 15 +- > 7 files changed, 395 insertions(+), 27 deletions(-) >
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