Re: [PATCH v5 5/5] perf-stat: introduce bpf_counter_ops->disable()

[Song Liu]

> On Apr 27, 2021, at 12:30 PM, Song Liu <songliubraving@xxxxxx> wrote:
> 
> 
> 
>> On Apr 27, 2021, at 5:33 AM, Jiri Olsa <jolsa@xxxxxxxxxx> 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@xxxxxxxxxx> 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).
> 

Would something like the following work? It is not clean (skipping some 
useful logic in __evlist__[enable|disable]). But it seems to work in the
tests.

Thanks,
Song