linux-kernel - Re: [kvm-unit-tests patch v6 08/18] x86: pmu: Fix cycles event validation failure

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Message-ID: <Z6-wrVaVSiI9ZKkD@google.com>
Date: Fri, 14 Feb 2025 13:07:57 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jim Mattson <jmattson@...gle.com>, Mingwei Zhang <mizhang@...gle.com>, 
	Xiong Zhang <xiong.y.zhang@...el.com>, Zhenyu Wang <zhenyuw@...ux.intel.com>, 
	Like Xu <like.xu.linux@...il.com>, Jinrong Liang <cloudliang@...cent.com>, 
	Yongwei Ma <yongwei.ma@...el.com>, Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [kvm-unit-tests patch v6 08/18] x86: pmu: Fix cycles event
 validation failure

On Sat, Sep 14, 2024, Dapeng Mi wrote:
> +static void warm_up(void)
> +{
> +	int i = 8;
> +
> +	/*
> +	 * Since cycles event is always run as the first event, there would be
> +	 * a warm-up state to warm up the cache, it leads to the measured cycles
> +	 * value may exceed the pre-defined cycles upper boundary and cause
> +	 * false positive. To avoid this, introduce an warm-up state before
> +	 * the real verification.
> +	 */
> +	while (i--)
> +		loop();

Use a for-loop.

> +}
> +
>  static void check_counters(void)
>  {
>  	if (is_fep_available())
>  		check_emulated_instr();
>  
> +	warm_up();
>  	check_gp_counters();
>  	check_fixed_counters();
>  	check_rdpmc();
> -- 
> 2.40.1
>