From: David Laight <david.laight.linux@gmail.com>
To: Ian Rogers <irogers@google.com>
Cc: "Peter Zijlstra" <peterz@infradead.org>,
"Ingo Molnar" <mingo@redhat.com>,
"Arnaldo Carvalho de Melo" <acme@kernel.org>,
"Namhyung Kim" <namhyung@kernel.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
"Jiri Olsa" <jolsa@kernel.org>,
"Adrian Hunter" <adrian.hunter@intel.com>,
"Kan Liang" <kan.liang@linux.intel.com>,
"Sam James" <sam@gentoo.org>,
"Jesper Juhl" <jesperjuhl76@gmail.com>,
"James Clark" <james.clark@linaro.org>,
"Zhongqiu Han" <quic_zhonhan@quicinc.com>,
"Yicong Yang" <yangyicong@hisilicon.com>,
"Thomas Richter" <tmricht@linux.ibm.com>,
"Michael Petlan" <mpetlan@redhat.com>,
"Veronika Molnarova" <vmolnaro@redhat.com>,
"Anne Macedo" <retpolanne@posteo.net>,
"Dominique Martinet" <asmadeus@codewreck.org>,
"Jean-Philippe Romain" <jean-philippe.romain@foss.st.com>,
"Junhao He" <hejunhao3@huawei.com>,
linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
"Krzysztof Łopatowski" <krzysztof.m.lopatowski@gmail.com>
Subject: Re: [PATCH v2 0/7] Add io_dir to avoid memory overhead from opendir
Date: Sat, 8 Feb 2025 10:58:21 +0000 [thread overview]
Message-ID: <20250208105821.1cdb54fc@pumpkin> (raw)
In-Reply-To: <20250207232452.994822-1-irogers@google.com>
On Fri, 7 Feb 2025 15:24:41 -0800
Ian Rogers <irogers@google.com> wrote:
> glibc's opendir allocates a minimum of 32kb, when called recursively
> for a directory tree the memory consumption can add up - nearly 300kb
> during perf start-up when processing modules. Add a stack allocated
> variant of readdir sized a little more than 1kb
Does 300kB really matter?
You seem to be trading memory allocation against system calls.
My 'gut feel' is that the system call cost will dominate.
(Unless all the directories are small.)
There might, of course, be other code in glibc that is designed
to make it all slower than necessary.
David
next prev parent reply other threads:[~2025-02-08 10:58 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-07 23:24 [PATCH v2 0/7] Add io_dir to avoid memory overhead from opendir Ian Rogers
2025-02-07 23:24 ` [PATCH v2 1/7] tools lib api: Add io_dir an allocation free readdir alternative Ian Rogers
2025-02-08 17:02 ` [PATCH v2 1/7] tools lib api: Add io_dir() as an allocation free readdir() alternative Markus Elfring
2025-02-19 21:51 ` [PATCH v2 1/7] tools lib api: Add io_dir an allocation free readdir alternative Namhyung Kim
2025-02-19 22:21 ` Ian Rogers
2025-02-21 6:31 ` Namhyung Kim
2025-02-07 23:24 ` [PATCH v2 2/7] perf maps: Switch modules tree walk to io_dir__readdir Ian Rogers
2025-02-07 23:24 ` [PATCH v2 3/7] perf pmu: Switch " Ian Rogers
2025-02-07 23:24 ` [PATCH v2 4/7] perf header: Switch mem topology " Ian Rogers
2025-02-07 23:24 ` [PATCH v2 5/7] perf events: Remove scandir in thread synthesis Ian Rogers
2025-02-07 23:24 ` [PATCH v2 6/7] perf parse-events: Switch tracepoints to io_dir__readdir Ian Rogers
2025-02-07 23:24 ` [PATCH v2 7/7] perf hwmon_pmu: Switch event discovery " Ian Rogers
2025-02-08 10:58 ` David Laight [this message]
2025-02-08 12:15 ` [PATCH v2 0/7] Add io_dir to avoid memory overhead from opendir Ian Rogers
2025-02-19 21:54 ` Namhyung Kim
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