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From: Ravi Bangoria <ravi.bangoria@amd.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: peterz@infradead.org, rrichter@amd.com, mingo@redhat.com,
	mark.rutland@arm.com, jolsa@kernel.org, namhyung@kernel.org,
	tglx@linutronix.de, bp@alien8.de, irogers@google.com,
	yao.jin@linux.intel.com, james.clark@arm.com, leo.yan@linaro.org,
	kan.liang@linux.intel.com, ak@linux.intel.com,
	eranian@google.com, like.xu.linux@gmail.com, x86@kernel.org,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	sandipan.das@amd.com, ananth.narayan@amd.com,
	kim.phillips@amd.com, santosh.shukla@amd.com,
	Ravi Bangoria <ravi.bangoria@amd.com>
Subject: Re: [PATCH v2 5/8] perf record ibs: Warn about sampling period skew
Date: Mon, 16 May 2022 18:57:11 +0530	[thread overview]
Message-ID: <11052843-8fff-a497-f34e-8e53f846fe7e@amd.com> (raw)
In-Reply-To: <YoJP+JqI2M1i647y@kernel.org>

On 16-May-22 6:52 PM, Arnaldo Carvalho de Melo wrote:
> Em Mon, May 09, 2022 at 10:19:11AM +0530, Ravi Bangoria escreveu:
>> Samples without an L3 miss are discarded and counter is reset with
>> random value (between 1-15 for fetch pmu and 1-127 for op pmu) when
>> IBS L3 miss filtering is enabled. This causes a sampling period skew
>> but there is no way to reconstruct aggregated sampling period. So
>> print a warning at perf record if user sets l3missonly=1.
>>
>> Ex:
>>   # perf record -c 10000 -C 0 -e ibs_op/l3missonly=1/
>>   WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled
>>   and tagged operation does not cause L3 Miss. This causes sampling period skew.
>>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
>> ---
>>  tools/perf/arch/x86/util/evsel.c | 34 ++++++++++++++++++++++++++++++++
>>  tools/perf/util/evsel.c          |  7 +++++++
>>  tools/perf/util/evsel.h          |  1 +
>>  3 files changed, 42 insertions(+)
>>
>> diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c
>> index ac2899a25b7a..6399faa70a88 100644
>> --- a/tools/perf/arch/x86/util/evsel.c
>> +++ b/tools/perf/arch/x86/util/evsel.c
>> @@ -4,6 +4,8 @@
>>  #include "util/evsel.h"
>>  #include "util/env.h"
>>  #include "linux/string.h"
>> +#include "util/pmu.h"
>> +#include "util/debug.h"
>>  
>>  void arch_evsel__set_sample_weight(struct evsel *evsel)
>>  {
>> @@ -29,3 +31,35 @@ void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr)
>>  
>>  	free(env.cpuid);
>>  }
>> +
>> +static void ibs_l3miss_warn(void)
>> +{
>> +	pr_warning(
>> +"WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled\n"
>> +"and tagged operation does not cause L3 Miss. This causes sampling period skew.\n");
>> +}
>> +
>> +void arch_evsel__warn_ambiguity(struct evsel *evsel, struct perf_event_attr *attr)
>> +{
>> +	struct perf_env *env = evsel__env(evsel);
>> +	struct perf_pmu *evsel_pmu = evsel__find_pmu(evsel);
>> +	struct perf_pmu *ibs_fetch_pmu = perf_pmu__find("ibs_fetch");
>> +	struct perf_pmu *ibs_op_pmu = perf_pmu__find("ibs_op");
>> +	static int warned_once;
> 
> Please check first if the warning was emitted (warned_once is true)
> before calling all the find routines above.

Sure.

> 
>> +	if (warned_once || !perf_env__cpuid(env) || !env->cpuid ||
>> +	    !strstarts(env->cpuid, "AuthenticAMD") || !evsel_pmu)
>> +		return;
>> +
>> +	if (ibs_fetch_pmu && ibs_fetch_pmu->type == evsel_pmu->type) {
>> +		if (attr->config & (1ULL << 59)) {
>> +			ibs_l3miss_warn();
>> +			warned_once = 1;
>> +		}
>> +	} else if (ibs_op_pmu && ibs_op_pmu->type == evsel_pmu->type) {
>> +		if (attr->config & (1ULL << 16)) {
>> +			ibs_l3miss_warn();
>> +			warned_once = 1;
>> +		}
>> +	}
>> +}
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 2a1729e7aee4..4f8b72d4a521 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -1064,6 +1064,11 @@ void __weak arch_evsel__fixup_new_cycles(struct perf_event_attr *attr __maybe_un
>>  {
>>  }
>>  
>> +void __weak arch_evsel__warn_ambiguity(struct evsel *evsel __maybe_unused,
>> +				       struct perf_event_attr *attr __maybe_unused)
>> +{
>> +}
>> +
>>  static void evsel__set_default_freq_period(struct record_opts *opts,
>>  					   struct perf_event_attr *attr)
>>  {
>> @@ -1339,6 +1344,8 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
>>  	 */
>>  	if (evsel__is_dummy_event(evsel))
>>  		evsel__reset_sample_bit(evsel, BRANCH_STACK);
>> +
>> +	arch_evsel__warn_ambiguity(evsel, attr);
> 
> Wouldn't this be better as a single arch__post_evsel_config() function that
> could do arch specific fixups or emit such warnings _after_ (thus the
> "post") the common code evsel__config() does its thing?

Will rename accordingly. 

Thanks,
Ravi

  reply	other threads:[~2022-05-16 13:27 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-09  4:49 [PATCH v2 0/8] perf/amd: Zen4 IBS extensions support Ravi Bangoria
2022-05-09  4:49 ` [PATCH v2 1/8] perf/amd/ibs: Cascade pmu init functions' return value Ravi Bangoria
2022-05-11 19:47   ` [tip: perf/core] " tip-bot2 for Ravi Bangoria
2022-05-09  4:49 ` [PATCH v2 2/8] perf/amd/ibs: Use ->is_visible callback for dynamic attributes Ravi Bangoria
2022-05-11 19:47   ` [tip: perf/core] " tip-bot2 for Ravi Bangoria
2022-05-09  4:49 ` [PATCH v2 3/8] perf/amd/ibs: Add support for L3 miss filtering Ravi Bangoria
2022-05-09 12:05   ` Peter Zijlstra
2022-05-09 12:35     ` Ravi Bangoria
2022-05-09 13:07       ` Peter Zijlstra
2022-05-11 19:46   ` [tip: perf/core] " tip-bot2 for Ravi Bangoria
2022-05-09  4:49 ` [PATCH v2 4/8] perf/amd/ibs: Advertise zen4_ibs_extensions as pmu capability attribute Ravi Bangoria
2022-05-11 19:46   ` [tip: perf/core] " tip-bot2 for Ravi Bangoria
2022-05-09  4:49 ` [PATCH v2 5/8] perf record ibs: Warn about sampling period skew Ravi Bangoria
2022-05-16 13:22   ` Arnaldo Carvalho de Melo
2022-05-16 13:27     ` Ravi Bangoria [this message]
2022-05-09  4:49 ` [PATCH v2 6/8] perf header: Parse non-cpu pmu capabilities Ravi Bangoria
2022-05-16  4:15   ` Ravi Bangoria
2022-05-16 12:53     ` Arnaldo Carvalho de Melo
2022-05-16 13:28   ` Arnaldo Carvalho de Melo
2022-05-16 13:46     ` Ravi Bangoria
2022-05-09  4:49 ` [PATCH v2 7/8] perf script ibs: Support new IBS bits in raw trace dump Ravi Bangoria
2022-05-16 13:29   ` Arnaldo Carvalho de Melo
2022-05-16 13:47     ` Ravi Bangoria
2022-05-09  4:49 ` [PATCH v2 8/8] perf ibs: Fix comment Ravi Bangoria
2022-05-11 19:46   ` [tip: perf/core] perf/ibs: " tip-bot2 for Ravi Bangoria

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