linux-kernel - Re: [PATCH v5 5/5] perf-stat: introduce bpf_counter

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Date:   Tue, 27 Apr 2021 19:30:28 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     Song Liu <song@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "acme@...nel.org" <acme@...nel.org>,
        "acme@...hat.com" <acme@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "jolsa@...nel.org" <jolsa@...nel.org>
Subject: Re: [PATCH v5 5/5] perf-stat: introduce bpf_counter_ops->disable()



> On Apr 27, 2021, at 5:33 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> 
> On Mon, Apr 26, 2021 at 10:18:57PM +0000, Song Liu wrote:
>> 
>> 
>>> On Apr 26, 2021, at 2:27 PM, Jiri Olsa <jolsa@...hat.com> wrote:
>>> 
>>> On Sun, Apr 25, 2021 at 02:43:33PM -0700, Song Liu wrote:
>>> 
>>> SNIP
>>> 
>>>> +static inline int bpf_counter__disable(struct evsel *evsel __maybe_unused)
>>>> +{
>>>> +	return 0;
>>>> +}
>>>> +
>>>> static inline int bpf_counter__read(struct evsel *evsel __maybe_unused)
>>>> {
>>>> 	return -EAGAIN;
>>>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>>>> index d29a8a118973c..e71041c890102 100644
>>>> --- a/tools/perf/util/evlist.c
>>>> +++ b/tools/perf/util/evlist.c
>>>> @@ -17,6 +17,7 @@
>>>> #include "evsel.h"
>>>> #include "debug.h"
>>>> #include "units.h"
>>>> +#include "bpf_counter.h"
>>>> #include <internal/lib.h> // page_size
>>>> #include "affinity.h"
>>>> #include "../perf.h"
>>>> @@ -421,6 +422,9 @@ static void __evlist__disable(struct evlist *evlist, char *evsel_name)
>>>> 	if (affinity__setup(&affinity) < 0)
>>>> 		return;
>>>> 
>>>> +	evlist__for_each_entry(evlist, pos)
>>>> +		bpf_counter__disable(pos);
>>> 
>>> I was wondering why you don't check evsel__is_bpf like
>>> for the enable case.. and realized that we don't skip
>>> bpf evsels in __evlist__enable and __evlist__disable
>>> like we do in read_affinity_counters
>>> 
>>> so I guess there's extra affinity setup and bunch of
>>> wrong ioctls being called?
>> 
>> We actually didn't do wrong ioctls because the following check:
>> 
>>       if (... || !pos->core.fd)
>>                continue;
>> 
>> in __evlist__enable and __evlist__disable. That we don't allocate 
>> core.fd for is_bpf events. 
>> 
>> It is probably good to be more safe with an extra check of 
>> evsel__is_bpf(). But it is not required with current code. 
> 
> hum, but it will do all the affinity setup no? for no reason,
> if there's no non-bpb event

Yes, it will do the affinity setup. Let me see how to get something
like all_counters_use_bpf here (or within builtin-stat.c).

Thanks,
Song