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

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Message-ID: <CDBE5630-F7F0-494D-BFA8-33742D831C2D@fb.com>
Date:   Mon, 26 Apr 2021 22:18:57 +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 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. 

Thanks,
Song

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