linux-kernel - Re: [PATCH RFC 02/10] perf tools: using scandir to replace readdir

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Message-ID: <20170908141107.GE11725@kernel.org>
Date:   Fri, 8 Sep 2017 11:11:07 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     kan.liang@...el.com
Cc:     peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, jolsa@...nel.org,
        namhyung@...nel.org, adrian.hunter@...el.com,
        lukasz.odzioba@...el.com, ak@...ux.intel.com
Subject: Re: [PATCH RFC 02/10] perf tools: using scandir to replace readdir

Em Thu, Sep 07, 2017 at 10:55:46AM -0700, kan.liang@...el.com escreveu:
> From: Kan Liang <kan.liang@...el.com>
> 
> For perf_event__synthesize_threads, perf goes through all proc files
> serially by readdir.
> scandir did a snapshoot of proc, which is multithreading friendly.
> 
> It's possible that some threads which are added during event synthesize.
> But the number of lost threads should be small.
> They should not impact the final analysis.

Looks ok, applied locally, will see how it builds in my containers
tests.

- Arnaldo
 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  tools/perf/util/event.c | 45 +++++++++++++++++++++++++--------------------
>  1 file changed, 25 insertions(+), 20 deletions(-)
> 
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index 1c905ba..17c21ea 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -683,12 +683,14 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
>  				   bool mmap_data,
>  				   unsigned int proc_map_timeout)
>  {
> -	DIR *proc;
> -	char proc_path[PATH_MAX];
> -	struct dirent *dirent;
>  	union perf_event *comm_event, *mmap_event, *fork_event;
>  	union perf_event *namespaces_event;
> +	char proc_path[PATH_MAX];
> +	struct dirent **dirent;
>  	int err = -1;
> +	char *end;
> +	pid_t pid;
> +	int n, i;
>  
>  	if (machine__is_default_guest(machine))
>  		return 0;
> @@ -712,29 +714,32 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
>  		goto out_free_fork;
>  
>  	snprintf(proc_path, sizeof(proc_path), "%s/proc", machine->root_dir);
> -	proc = opendir(proc_path);
> +	n = scandir(proc_path, &dirent, 0, alphasort);
>  
> -	if (proc == NULL)
> +	if (n < 0)
>  		goto out_free_namespaces;
>  
> -	while ((dirent = readdir(proc)) != NULL) {
> -		char *end;
> -		pid_t pid = strtol(dirent->d_name, &end, 10);
> -
> -		if (*end) /* only interested in proper numerical dirents */
> +	for (i = 0; i < n; i++) {
> +		if (!isdigit(dirent[i]->d_name[0]))
>  			continue;
> -		/*
> - 		 * We may race with exiting thread, so don't stop just because
> - 		 * one thread couldn't be synthesized.
> - 		 */
> -		__event__synthesize_thread(comm_event, mmap_event, fork_event,
> -					   namespaces_event, pid, 1, process,
> -					   tool, machine, mmap_data,
> -					   proc_map_timeout);
> -	}
>  
> +		pid = (pid_t)strtol(dirent[i]->d_name, &end, 10);
> +		/* only interested in proper numerical dirents */
> +		if (!*end) {
> +			/*
> +			 * We may race with exiting thread, so don't stop just because
> +			 * one thread couldn't be synthesized.
> +			 */
> +			__event__synthesize_thread(comm_event, mmap_event, fork_event,
> +						   namespaces_event, pid, 1, process,
> +						   tool, machine, mmap_data,
> +						   proc_map_timeout);
> +		}
> +		free(dirent[i]);
> +	}
> +	free(dirent);
>  	err = 0;
> -	closedir(proc);
> +
>  out_free_namespaces:
>  	free(namespaces_event);
>  out_free_fork:
> -- 
> 2.5.5