Messages in this thread | | | Subject | Re: [PATCH V7 03/18] perf/x86/intel: Handle guest PEBS overflow PMI for KVM guest | From | "Zhu, Lingshan" <> | Date | Thu, 8 Jul 2021 21:39:50 +0800 |
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On 7/2/2021 7:28 PM, Peter Zijlstra wrote: > On Tue, Jun 22, 2021 at 05:42:51PM +0800, Zhu Lingshan wrote: >> +DECLARE_STATIC_CALL(x86_guest_state, *(perf_guest_cbs->state)); >> + >> +/* >> + * We may be running with guest PEBS events created by KVM, and the >> + * PEBS records are logged into the guest's DS and invisible to host. >> + * >> + * In the case of guest PEBS overflow, we only trigger a fake event >> + * to emulate the PEBS overflow PMI for guest PBES counters in KVM. >> + * The guest will then vm-entry and check the guest DS area to read >> + * the guest PEBS records. >> + * >> + * The contents and other behavior of the guest event do not matter. >> + */ >> +static void x86_pmu_handle_guest_pebs(struct pt_regs *regs, >> + struct perf_sample_data *data) >> +{ >> + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); >> + u64 guest_pebs_idxs = cpuc->pebs_enabled & ~cpuc->intel_ctrl_host_mask; >> + struct perf_event *event = NULL; >> + unsigned int guest = 0; >> + int bit; >> + >> + if (!x86_pmu.pebs_vmx || !x86_pmu.pebs_active || >> + !(cpuc->pebs_enabled & ~cpuc->intel_ctrl_host_mask)) >> + return; >> + >> + guest = static_call(x86_guest_state)(); >> + if (!(guest & PERF_GUEST_ACTIVE)) >> + return; > I think you've got the branches the wrong way around here; nobody runs a > VM so this branch will get you out without a load. > > Only if you're one of those daft people running a VM, are you interested > in any of the other conditions that are required. > > Also, I think both pebs_active and pebs_vmx can he a static_branch, but > that can be done later I suppose. Hi Peter,
If I understand this correctly, are you suggesting we put "if (!(guest & PERF_GUEST_ACTIVE))" first because this is a lower cost branch?
Thanks, Zhu Lingshan
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