linux-kernel - Re: [PATCH v3 1/7] perf pmu: Use file system cache to optimize sysfs access

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Message-ID: <20191029021419.GT4660@tassilo.jf.intel.com>
Date:   Mon, 28 Oct 2019 19:14:19 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andi Kleen <andi@...stfloor.org>, acme@...nel.org,
        jolsa@...nel.org, eranian@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/7] perf pmu: Use file system cache to optimize sysfs
 access

On Mon, Oct 28, 2019 at 11:01:37PM +0100, Jiri Olsa wrote:
> On Fri, Oct 25, 2019 at 11:14:11AM -0700, Andi Kleen wrote:
> 
> SNIP
> 
> >  	if (pmu_aliases_parse(path, head))
> >  		return -1;
> > @@ -525,7 +524,6 @@ static int pmu_alias_terms(struct perf_pmu_alias *alias,
> >   */
> >  static int pmu_type(const char *name, __u32 *type)
> >  {
> > -	struct stat st;
> >  	char path[PATH_MAX];
> >  	FILE *file;
> >  	int ret = 0;
> > @@ -537,7 +535,7 @@ static int pmu_type(const char *name, __u32 *type)
> >  	snprintf(path, PATH_MAX,
> >  		 "%s" EVENT_SOURCE_DEVICE_PATH "%s/type", sysfs, name);
> >  
> > -	if (stat(path, &st) < 0)
> > +	if (access(path, R_OK) < 0)
> 
> why not file_available call in here?

iirc it doesn't do any redundant accesses.

-Andi