linux-kernel - Re: [PATCH] perf kvm: fix sample

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Date:	Fri, 6 Sep 2013 09:53:04 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf kvm: fix sample_type manipulation

Em Fri, Sep 06, 2013 at 09:48:54AM +0300, Adrian Hunter escreveu:
> Manipulating the sample_type of an evsel requires
> the use of:
> 	perf_evsel__set_sample_bit()
> and	perf_evsel__reset_sample_bit()

Fine, but...
 
> Manipulating the sample type of an evlist requires
> the id position to be recalculated.

... can't we hide this detail? I.e. we could do it like we do with the
alloc_{mmap,poll}() evlist methods in perf_evlist__mmap(), checking if it was
already done, etc.

This we reduce the contact surface for tools using evlists and evsels.

I.e., this sequence:

 
+	perf_evlist__set_id_pos(evlist);
+
 	err = perf_evlist__open(evlist);

Could remain just:

	err = perf_evlist__open(evlist);

I'm auditing the other calls to evlist now, to check if there are other cases.

Thanks for the patch!

- Arnaldo

 
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
>  tools/perf/builtin-kvm.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c
> index 47b3540..0b7c5a9 100644
> --- a/tools/perf/builtin-kvm.c
> +++ b/tools/perf/builtin-kvm.c
> @@ -1165,16 +1165,16 @@ static int kvm_live_open_events(struct perf_kvm_stat *kvm)
>  		struct perf_event_attr *attr = &pos->attr;
>  
>  		/* make sure these *are* set */
> -		attr->sample_type |= PERF_SAMPLE_TID;
> -		attr->sample_type |= PERF_SAMPLE_TIME;
> -		attr->sample_type |= PERF_SAMPLE_CPU;
> -		attr->sample_type |= PERF_SAMPLE_RAW;
> +		perf_evsel__set_sample_bit(pos, TID);
> +		perf_evsel__set_sample_bit(pos, TIME);
> +		perf_evsel__set_sample_bit(pos, CPU);
> +		perf_evsel__set_sample_bit(pos, RAW);
>  		/* make sure these are *not*; want as small a sample as possible */
> -		attr->sample_type &= ~PERF_SAMPLE_PERIOD;
> -		attr->sample_type &= ~PERF_SAMPLE_IP;
> -		attr->sample_type &= ~PERF_SAMPLE_CALLCHAIN;
> -		attr->sample_type &= ~PERF_SAMPLE_ADDR;
> -		attr->sample_type &= ~PERF_SAMPLE_READ;
> +		perf_evsel__reset_sample_bit(pos, PERIOD);
> +		perf_evsel__reset_sample_bit(pos, IP);
> +		perf_evsel__reset_sample_bit(pos, CALLCHAIN);
> +		perf_evsel__reset_sample_bit(pos, ADDR);
> +		perf_evsel__reset_sample_bit(pos, READ);
>  		attr->mmap = 0;
>  		attr->comm = 0;
>  		attr->task = 0;
> @@ -1188,6 +1188,8 @@ static int kvm_live_open_events(struct perf_kvm_stat *kvm)
>  		attr->disabled = 1;
>  	}
>  
> +	perf_evlist__set_id_pos(evlist);
> +
>  	err = perf_evlist__open(evlist);
>  	if (err < 0) {
>  		printf("Couldn't create the events: %s\n", strerror(errno));
> -- 
> 1.7.11.7
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