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

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Message-ID: <add089ff-49d9-40a9-a020-5f4eb876aef8@linux.intel.com>
Date: Tue, 18 Feb 2025 17:36:19 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.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>,
 Like Xu <like.xu.linux@...il.com>, Jinrong Liang <cloudliang@...cent.com>,
 Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [kvm-unit-tests patch v6 08/18] x86: pmu: Fix cycles event
 validation failure


On 2/15/2025 5:07 AM, Sean Christopherson wrote:
> 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.

Sure.


>
>> +}
>> +
>>  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
>>