linux-kernel - Re: [kvm-unit-tests Patch v3 08/11] x86: pmu: Improve instruction and branches events verification

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Date: Wed, 27 Mar 2024 06:14:58 +0000
From: Mingwei Zhang <mizhang@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Jim Mattson <jmattson@...gle.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Zhenyu Wang <zhenyuw@...ux.intel.com>,
	Zhang Xiong <xiong.y.zhang@...el.com>,
	Like Xu <like.xu.linux@...il.com>,
	Jinrong Liang <cloudliang@...cent.com>,
	Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [kvm-unit-tests Patch v3 08/11] x86: pmu: Improve instruction
 and branches events verification

On Wed, Jan 03, 2024, Dapeng Mi wrote:
> If HW supports GLOBAL_CTRL MSR, enabling and disabling PMCs are moved in
> __precise_count_loop(). Thus, instructions and branches events can be
> verified against a precise count instead of a rough range.
> 
> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> ---
>  x86/pmu.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/x86/pmu.c b/x86/pmu.c
> index 88b89ad889b9..b764827c1c3d 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -25,6 +25,10 @@
>  	"nop; nop; nop; nop; nop; nop; nop;\n\t"	\
>  	"loop 1b;\n\t"
>  
> +/*Enable GLOBAL_CTRL + disable GLOBAL_CTRL instructions */
> +#define PRECISE_EXTRA_INSTRNS  (2 + 4)
> +#define PRECISE_LOOP_INSTRNS   (N * LOOP_INSTRNS + PRECISE_EXTRA_INSTRNS)
> +#define PRECISE_LOOP_BRANCHES  (N)
>  #define PRECISE_LOOP_ASM						\
>  	"wrmsr;\n\t"							\
>  	"mov %%ecx, %%edi; mov %%ebx, %%ecx;\n\t"			\
> @@ -107,6 +111,24 @@ static inline void loop(u64 cntrs)
>  		__precise_count_loop(cntrs);
>  }
>  
> +static void adjust_events_range(struct pmu_event *gp_events, int branch_idx)
> +{
> +	/*
> +	 * If HW supports GLOBAL_CTRL MSR, enabling and disabling PMCs are
> +	 * moved in __precise_count_loop(). Thus, instructions and branches
> +	 * events can be verified against a precise count instead of a rough
> +	 * range.
> +	 */
> +	if (this_cpu_has_perf_global_ctrl()) {
> +		/* instructions event */
> +		gp_events[0].min = PRECISE_LOOP_INSTRNS;
> +		gp_events[0].max = PRECISE_LOOP_INSTRNS;
> +		/* branches event */
> +		gp_events[branch_idx].min = PRECISE_LOOP_BRANCHES;
> +		gp_events[branch_idx].max = PRECISE_LOOP_BRANCHES;
> +	}
> +}
> +
>  volatile uint64_t irq_received;
>  
>  static void cnt_overflow(isr_regs_t *regs)
> @@ -771,6 +793,7 @@ static void check_invalid_rdpmc_gp(void)
>  
>  int main(int ac, char **av)
>  {
> +	int branch_idx;
>  	setup_vm();
>  	handle_irq(PMI_VECTOR, cnt_overflow);
>  	buf = malloc(N*64);
> @@ -784,13 +807,16 @@ int main(int ac, char **av)
>  		}
>  		gp_events = (struct pmu_event *)intel_gp_events;
>  		gp_events_size = sizeof(intel_gp_events)/sizeof(intel_gp_events[0]);
> +		branch_idx = 5;

This (and the follow up one) hardcoded index is hacky and more
importantly, error prone especially when code get refactored later.
Please use a proper way via macro? Eg., checking
INTEL_ARCH_BRANCHES_RETIRED_INDEX in pmu_counters_test.c might be a good
one.
>  		report_prefix_push("Intel");
>  		set_ref_cycle_expectations();
>  	} else {
>  		gp_events_size = sizeof(amd_gp_events)/sizeof(amd_gp_events[0]);
>  		gp_events = (struct pmu_event *)amd_gp_events;
> +		branch_idx = 2;
>  		report_prefix_push("AMD");
>  	}
> +	adjust_events_range(gp_events, branch_idx);
>  
>  	printf("PMU version:         %d\n", pmu.version);
>  	printf("GP counters:         %d\n", pmu.nr_gp_counters);
> -- 
> 2.34.1
>