linux-kernel - Re: [UNTESTED][PATCH] perf/x86: Fix limit

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Message-ID: <5f2c62d4-1bfa-458d-847e-095979a4bf54@amd.com>
Date: Thu, 16 Jan 2025 09:51:33 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
 namhyung@...nel.org, eranian@...gle.com, irogers@...gle.com, bp@...en8.de,
 x86@...nel.org, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org, santosh.shukla@....com,
 ananth.narayan@....com, sandipan.das@....com,
 Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [UNTESTED][PATCH] perf/x86: Fix limit_period() for 'freq mode
 events'

>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
>> index c75c482d4c52..924aa35676d3 100644
>> --- a/arch/x86/events/core.c
>> +++ b/arch/x86/events/core.c
>> @@ -629,10 +629,22 @@ int x86_pmu_hw_config(struct perf_event *event)
>>  		event->hw.config |= x86_pmu_get_event_config(event);
>>  
>>  	if (event->attr.sample_period && x86_pmu.limit_period) {
>> -		s64 left = event->attr.sample_period;
>> -		x86_pmu.limit_period(event, &left);
>> -		if (left > event->attr.sample_period)
>> -			return -EINVAL;
>> +		if (event->attr.freq) {
>> +			s64 left = event->hw.sample_period;
>> +
>> +			x86_pmu.limit_period(event, &left);
>> +			if (left != event->hw.sample_period) {
>> +				event->hw.sample_period = left;
>> +				event->hw.last_period = left;
>> +				local64_set(&event->hw.period_left, left);
>> +			}
> 
> For a better start period, I'd prefer the below patch.
> https://lore.kernel.org/lkml/20241022130414.2493923-1-kan.liang@linux.intel.com/
> 
> The limit_period() check was introduced in the c46e665f0377 ("perf/x86:
> Add INST_RETIRED.ALL workarounds"). For my understanding, it's to check
> the !freq case. If so, I'm thinking something as below.
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index 79a4aad5a0a3..6467ecc65486 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -630,7 +630,7 @@ int x86_pmu_hw_config(struct perf_event *event)
>  	if (event->attr.type == event->pmu->type)
>  		event->hw.config |= x86_pmu_get_event_config(event);
> 
> -	if (event->attr.sample_period && x86_pmu.limit_period) {
> +	if (!event->attr.freq && x86_pmu.limit_period) {
>  		s64 left = event->attr.sample_period;
>  		x86_pmu.limit_period(event, &left);
>  		if (left > event->attr.sample_period)

LGTM.

>> +		} else {
>> +			s64 left = event->attr.sample_period;
>> +
>> +			x86_pmu.limit_period(event, &left);
>> +			if (left > event->attr.sample_period)
>> +				return -EINVAL;
>> +		}
>>  	}
>>  
>>  	/* sample_regs_user never support XMM registers */
>> @@ -2648,6 +2660,9 @@ static int x86_pmu_check_period(struct perf_event *event, u64 value)
>>  	if (x86_pmu.check_period && x86_pmu.check_period(event, value))
>>  		return -EINVAL;
>>  
>> +	if (event->attr.freq)
>> +		return 0;
>> +
> 
> The ioctl(PERF_EVENT_IOC_PERIOD) can be used to set both freq and
> period. But according to the implementation, yes, the
> perf_event_check_period() should be only for the !freq mode.
> 
> If so, we may change the generic code.
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index f91ba29048ce..a9a04d4f3619 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -5960,14 +5960,15 @@ static int _perf_event_period(struct perf_event
> *event, u64 value)
>  	if (!value)
>  		return -EINVAL;
> 
> -	if (event->attr.freq && value > sysctl_perf_event_sample_rate)
> -		return -EINVAL;
> -
> -	if (perf_event_check_period(event, value))
> -		return -EINVAL;
> -
> -	if (!event->attr.freq && (value & (1ULL << 63)))
> -		return -EINVAL;
> +	if (event->attr.freq) {
> +		if (value > sysctl_perf_event_sample_rate)
> +			return -EINVAL;
> +	} else {
> +		if (perf_event_check_period(event, value))
> +			return -EINVAL;
> +		if (value & (1ULL << 63))
> +			return -EINVAL;
> +	}
> 
>  	event_function_call(event, __perf_event_period, &value);

LGTM. And you can remove the if (event->attr.freq) check from
intel_pmu_has_bts_period().

Mind sending a proper patch series?

Thanks,
Ravi