Re: [PATCH] perf topdown: Correct leader selection with sample_read enabled

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 6/27/2024 11:11 PM, Liang, Kan wrote:
> Hi Dapeng,
>
> On 2024-06-14 5:39 p.m., Dapeng Mi wrote:
>> Addresses an issue where, in the absence of a topdown metrics event
>> within a sampling group, the slots event was incorrectly bypassed as
>> the sampling leader when sample_read was enabled.
>>
>> perf record -e '{slots,branches}:S' -c 10000 -vv sleep 1
>>
>> In this case, the slots event should be sampled as leader but the
>> branches event is sampled in fact like the verbose output shows.
>>
>> perf_event_attr:
>>   type                             4 (cpu)
>>   size                             168
>>   config                           0x400 (slots)
>>   sample_type                      IP|TID|TIME|READ|CPU|IDENTIFIER
>>   read_format                      ID|GROUP|LOST
>>   disabled                         1
>>   sample_id_all                    1
>>   exclude_guest                    1
>> ------------------------------------------------------------
>> sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0x8 = 5
>> ------------------------------------------------------------
>> perf_event_attr:
>>   type                             0 (PERF_TYPE_HARDWARE)
>>   size                             168
>>   config                           0x4 (PERF_COUNT_HW_BRANCH_INSTRUCTIONS)
>>   { sample_period, sample_freq }   10000
>>   sample_type                      IP|TID|TIME|READ|CPU|IDENTIFIER
>>   read_format                      ID|GROUP|LOST
>>   sample_id_all                    1
>>   exclude_guest                    1
>>
>> The sample period of slots event instead of branches event is reset to
>> 0.
>>
>> This fix ensures the slots event remains the leader under these
>> conditions.
> This should be just one of the issues with the slots/topdown related
> sampling read.
>
> If adding one more topdown event, the sampling read may still be broken.
>  perf record -e "{slots,instructions,topdown-retiring}:S"  -C0 sleep 1
>  WARNING: events were regrouped to match PMUs
>  Error:
>  The sys_perf_event_open() syscall returned with 22 (Invalid argument)
> for event (topdown-retiring).
>
> That may require Yanfei's patch.
> https://lore.kernel.org/lkml/20240411144852.2507143-1-yanfei.xu@intel.com/

Yes, we need this patch. It would fix the error what you see.


>
> Please give it try and summarize all the required patches for the
> topdown sampling read feature.

I would talk with Yanfei, and collect all required patches into a whole
patchset. This would make the patch review more easily.


>
> Besides, we need a test for the sampling read as well.
> Ian has provided a very good base. Please add a topdown sampling read
> case on top of it as well.
> https://lore.kernel.org/lkml/CAP-5=fUkg-cAXTb+3wbFOQCfdXgpQeZw40XHjfrNFbnBD=NMXg@mail.gmail.com/

Sure. I would look at it and add a test case.


>
>
> Thanks,
> Kan
>
>> Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
>> ---
>>  tools/perf/arch/x86/util/topdown.c | 42 ++++++++++++++++++++++++++++--
>>  1 file changed, 40 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/arch/x86/util/topdown.c b/tools/perf/arch/x86/util/topdown.c
>> index 3f9a267d4501..aea6896bbb57 100644
>> --- a/tools/perf/arch/x86/util/topdown.c
>> +++ b/tools/perf/arch/x86/util/topdown.c
>> @@ -1,6 +1,7 @@
>>  // SPDX-License-Identifier: GPL-2.0
>>  #include "api/fs/fs.h"
>>  #include "util/evsel.h"
>> +#include "util/evlist.h"
>>  #include "util/pmu.h"
>>  #include "util/pmus.h"
>>  #include "util/topdown.h"
>> @@ -31,6 +32,32 @@ bool topdown_sys_has_perf_metrics(void)
>>  	return has_perf_metrics;
>>  }
>>  
>> +static int perf_pmus__topdown_event(void *vstate, struct pmu_event_info *info)
>> +{
>> +	if (!strcmp(info->name, (char *)vstate))
>> +		return 1;
>> +
>> +	return 0;
>> +}
>> +
>> +static bool is_topdown_metric_event(struct evsel *event)
>> +{
>> +	struct perf_pmu *pmu;
>> +
>> +	if (!topdown_sys_has_perf_metrics())
>> +		return false;
>> +
>> +	if (event->core.attr.type != PERF_TYPE_RAW)
>> +		return false;
>> +
>> +	pmu = perf_pmus__find_by_type(PERF_TYPE_RAW);
>> +	if (pmu && perf_pmu__for_each_event(pmu, false, event->name,
>> +					    perf_pmus__topdown_event))
>> +		return true;
>> +
>> +	return false;
>> +}
>> +
>>  #define TOPDOWN_SLOTS		0x0400
>>  
>>  /*
>> @@ -41,11 +68,22 @@ bool topdown_sys_has_perf_metrics(void)
>>   */
>>  bool arch_topdown_sample_read(struct evsel *leader)
>>  {
>> +	struct evsel *event;
>> +
>>  	if (!evsel__sys_has_perf_metrics(leader))
>>  		return false;
>>  
>> -	if (leader->core.attr.config == TOPDOWN_SLOTS)
>> -		return true;
>> +	if (leader->core.attr.config != TOPDOWN_SLOTS)
>> +		return false;
>> +
>> +	/*
>> +	 * If slots event as leader event but no topdown metric events in group,
>> +	 * slots event should still sample as leader.
>> +	 */
>> +	evlist__for_each_entry(leader->evlist, event) {
>> +		if (event != leader && is_topdown_metric_event(event))
>> +			return true;
>> +	}
>>  
>>  	return false;
>>  }
>>
>> base-commit: 92e5605a199efbaee59fb19e15d6cc2103a04ec2