linux-kernel - Re: [PATCH 08/17] perf record: Don't poll on overwrite channel

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Date:	Fri, 13 May 2016 10:12:09 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	arnaldo.melo@...il.com, linux-kernel@...r.kernel.org,
	He Kuang <hekuang@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.com>, pi3orama@....com
Subject: Re: [PATCH 08/17] perf record: Don't poll on overwrite channel

Em Fri, May 13, 2016 at 07:56:05AM +0000, Wang Nan escreveu:
> There's no need to receive events from overwritable ring buffer. Instead,
> perf should make them run background until something happen. This patch
> makes normal events from overwrite ring buffer ignored.
> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Signed-off-by: He Kuang <hekuang@...wei.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: pi3orama@....com
> ---
>  tools/perf/util/evlist.c | 23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index abce588..f0b0457 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -461,9 +461,9 @@ int perf_evlist__alloc_pollfd(struct perf_evlist *evlist)
>  	return 0;
>  }
>  
> -static int __perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd, int idx)
> +static int __perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd, int idx, short revent)
>  {
> -	int pos = fdarray__add(&evlist->pollfd, fd, POLLIN | POLLERR | POLLHUP);
> +	int pos = fdarray__add(&evlist->pollfd, fd, revent | POLLERR | POLLHUP);
>  	/*
>  	 * Save the idx so that when we filter out fds POLLHUP'ed we can
>  	 * close the associated evlist->mmap[] entry.
> @@ -479,7 +479,7 @@ static int __perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd, int idx
>  
>  int perf_evlist__add_pollfd(struct perf_evlist *evlist, int fd)
>  {
> -	return __perf_evlist__add_pollfd(evlist, fd, -1);
> +	return __perf_evlist__add_pollfd(evlist, fd, -1, POLLIN);
>  }
>  
>  static void perf_evlist__munmap_filtered(struct fdarray *fda, int fd)
> @@ -1077,6 +1077,18 @@ perf_evlist__channel_complete(struct perf_evlist *evlist)
>  	return 0;
>  }
>  
> +static bool
> +perf_evlist__should_poll(struct perf_evlist *evlist,
> +			 struct perf_evsel *evsel,
> +			 int channel)
> +{
> +	if (evsel->system_wide)
> +		return false;

So, what is the above doing in this patch? If we should not poll when in
syswide mode, then this should be in a separate patch, unrelated to
'channels'.  No?

I.e. it would be an improvement that would be cherry pickable right now,
even before reviewing the channel concept.

- Arnaldo

> +	if (perf_evlist__channel_check(evlist, channel, RDONLY))
> +		return false;
> +	return true;
> +}
> +
>  static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int _idx,
>  				       struct mmap_params *mp, int cpu,
>  				       int thread, int *outputs)
> @@ -1085,6 +1097,7 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int _idx,
>  
>  	evlist__for_each(evlist, evsel) {
>  		int fd, channel, idx, err;
> +		short revent = POLLIN;
>  
>  		channel = perf_evlist__channel_find(evlist, evsel, false);
>  		if (channel < 0) {
> @@ -1114,6 +1127,8 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int _idx,
>  			perf_evlist__mmap_get(evlist, idx);
>  		}
>  
> +		if (!perf_evlist__should_poll(evlist, evsel, channel))
> +			revent = 0;
>  		/*
>  		 * The system_wide flag causes a selected event to be opened
>  		 * always without a pid.  Consequently it will never get a
> @@ -1122,7 +1137,7 @@ static int perf_evlist__mmap_per_evsel(struct perf_evlist *evlist, int _idx,
>  		 * Therefore don't add it for polling.
>  		 */
>  		if (!evsel->system_wide &&
> -		    __perf_evlist__add_pollfd(evlist, fd, idx) < 0) {
> +		    __perf_evlist__add_pollfd(evlist, fd, idx, revent) < 0) {
>  			perf_evlist__mmap_put(evlist, idx);
>  			return -1;
>  		}
> -- 
> 1.8.3.4