linux-kernel - Re: [RFCv2 4/4] perf: util: support sysfs supported

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Message-ID: <20160718171303.GI10069@leverpostej>
Date:	Mon, 18 Jul 2016 18:13:03 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:	linux-kernel@...r.kernel.org, acme@...nel.org,
	adrian.hunter@...el.com, alexander.shishkin@...ux.intel.com,
	hekuang@...wei.com, jolsa@...nel.org, kan.liang@...el.com,
	mingo@...hat.com, peterz@...radead.org, wangnan0@...wei.com
Subject: Re: [RFCv2 4/4] perf: util: support sysfs supported_cpumask file

On Mon, Jul 18, 2016 at 05:38:16PM +0100, Suzuki K Poulose wrote:
> On 15/07/16 11:08, Mark Rutland wrote:
> >For system PMUs, the perf tools have long expected a cpumask file under
> >sysfs, describing the single CPU which they support events being
> >opened/handled on. Prior patches in this series have reworked this
> >support to support multiple CPUs in a mask, as is required to handle
> >heterogeneous CPU PMUs.
> >
> >Unfortunately, adding a cpumask file to CPU PMUs would break existing
> >userspace. Prior to this series, perf record will refuse to open events,
> >and perf stat may unexpectedly block at exit time. In the absence of a
> >cpumask, perf stat is functional.
> >
> >To address this, this patch adds support for a new file,
> >supported_cpumask, which can be used to describe heterogeneous CPUs,
> >without the risk of breaking existing userspace binaries.
> >
> >Signed-off-by: Mark Rutland <mark.rutland@....com>
> >---
> > tools/perf/util/pmu.c | 15 ++++++++++++---
> > 1 file changed, 12 insertions(+), 3 deletions(-)
> >
> >diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> >index ddb0261..06c985c 100644
> >--- a/tools/perf/util/pmu.c
> >+++ b/tools/perf/util/pmu.c
> >@@ -445,14 +445,23 @@ static struct cpu_map *pmu_cpumask(const char *name)
> > 	FILE *file;
> > 	struct cpu_map *cpus;
> > 	const char *sysfs = sysfs__mountpoint();
> >+	const char *path_template[] = {
> >+		 "%s/bus/event_source/devices/%s/cpumask",
> >+		 "%s/bus/event_source/devices/%s/supported_cpumask",
> >+		 NULL
> >+	};
> >+	unsigned int i;
> >
> > 	if (!sysfs)
> > 		return NULL;
> >
> >-	snprintf(path, PATH_MAX,
> >-		 "%s/bus/event_source/devices/%s/cpumask", sysfs, name);
> >+	for (i = 0; i < ARRAY_SIZE(path_template); i++) {
> 
> The check could be "path_template[i]" to avoid an iteration with NULL
> template.

True. I'd reworked this loop a few times to try to avoid duplicated
checks, but evidently I'd messed that up. I'll clean this up.

> 
> >+		snprintf(path, PATH_MAX, *path_template, sysfs, name);
> 
> Btw, did you mean to use path_template[i] here instead of *path_template ?
> 
> >+		if (stat(path, &st) == 0)
> >+			break;
> >+	}
> >
> >-	if (stat(path, &st) < 0)
> >+	if (!*path_template)
> 
> Same here ?

Yes. On both counts I meant to use the current iteration's entry.

Thanks for spotting that. I'll fix that up.

Thanks,
Mark.