Commit 74c504a6 authored Nov 04, 2019 by Andrea Arcangeli Committed by Paolo Bonzini Nov 15, 2019

x86: retpolines: eliminate retpoline from msr event handlers



It's enough to check the value and issue the direct call.

After this commit is applied, here the most common retpolines executed
under a high resolution timer workload in the guest on a VMX host:

[..]
@[
    trace_retpoline+1
    __trace_retpoline+30
    __x86_indirect_thunk_rax+33
    do_syscall_64+89
    entry_SYSCALL_64_after_hwframe+68
]: 267
@[]: 2256
@[
    trace_retpoline+1
    __trace_retpoline+30
    __x86_indirect_thunk_rax+33
    __kvm_wait_lapic_expire+284
    vmx_vcpu_run.part.97+1091
    vcpu_enter_guest+377
    kvm_arch_vcpu_ioctl_run+261
    kvm_vcpu_ioctl+559
    do_vfs_ioctl+164
    ksys_ioctl+96
    __x64_sys_ioctl+22
    do_syscall_64+89
    entry_SYSCALL_64_after_hwframe+68
]: 2390
@[]: 33410

@total: 315707

Note the highest hit above is __delay so probably not worth optimizing
even if it would be more frequent than 2k hits per sec.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 3dcb2a3f

arch/x86/events/intel/core.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -3323,8 +3323,19 @@ static int intel_pmu_hw_config(struct perf_event *event)
		return 0;
		}

		#ifdef CONFIG_RETPOLINE
		static struct perf_guest_switch_msr core_guest_get_msrs(int nr);
		static struct perf_guest_switch_msr intel_guest_get_msrs(int nr);
		#endif

		struct perf_guest_switch_msr perf_guest_get_msrs(int nr)
		{
		#ifdef CONFIG_RETPOLINE
		if (x86_pmu.guest_get_msrs == intel_guest_get_msrs)
		return intel_guest_get_msrs(nr);
		else if (x86_pmu.guest_get_msrs == core_guest_get_msrs)
		return core_guest_get_msrs(nr);
		#endif
		if (x86_pmu.guest_get_msrs)
		return x86_pmu.guest_get_msrs(nr);
		*nr = 0;

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