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From: Namhyung Kim <namhyung@kernel.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>, Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Stephane Eranian <eranian@google.com>,
	Ian Rogers <irogers@google.com>, Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH 3/3] tools/lib/fs: Cache cgroupfs mount point
Date: Thu, 21 Jan 2021 13:33:37 +0900	[thread overview]
Message-ID: <CAM9d7ci5W06UNthEBBs=-wJLjusO=bpFg2sFj=M0W3h20+oaHA@mail.gmail.com> (raw)
In-Reply-To: <CAM9d7chBmkG6S1QzF+gDU8=5ce8zQo2xM5Jr1t_iptsh_+t7NQ@mail.gmail.com>

Hi Arnaldo,

Can you share your thoughts on this?

On Fri, Jan 8, 2021 at 2:51 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> On Wed, Jan 6, 2021 at 10:33 AM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > Hi Arnaldo,
> >
> > On Tue, Dec 29, 2020 at 8:51 PM Arnaldo Carvalho de Melo
> > <acme@kernel.org> wrote:
> > >
> > > Em Wed, Dec 16, 2020 at 06:05:56PM +0900, Namhyung Kim escreveu:
> > > > Currently it parses the /proc file everytime it opens a file in the
> > > > cgroupfs.  Save the last result to avoid it (assuming it won't be
> > > > changed between the accesses).
> > >
> > > Which is the most likely case, but can't we use something like inotify
> > > to detect that and bail out or warn the user?
> >
> > Hmm.. looks doable.  Will check.
>
> So I've played with inotify a little bit, and it seems it needs to monitor
> changes on the file or the directory.  I didn't get any notification from
> the /proc/mounts file even if I did some mount/umount.
>
> Instead, I could get IN_UNMOUNT when the cgroup filesystem was
> unmounted.  But for the monitoring, we need to do one of a) select-like
> syscall to wait for the events, b) signal-driven IO notification or c) read
> the inotify file with non-block mode everytime.
>
> In a library code, I don't think we can do a) or b) since it can affect
> user program behaviors.  Then we should go with c) but I think
> it's opposite to the purpose of this patch. :)
>
> As you said, I think mostly we don't care as the accesses will happen
> in a short period of time.  But if you really care, maybe for the upcoming
> perf daemon changes, I think we can add an API to invalidate the cache
> or internal time-based invalidation logic (like remove it after 10 sec.).
>
> Thoughts?
>
> Thanks,
> Namhyung

  reply	other threads:[~2021-01-21  4:35 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-16  9:05 [PATCH 1/3] tools/lib/fs: Prefer cgroup v1 path Namhyung Kim
2020-12-16  9:05 ` [PATCH 2/3] tools/lib/fs: Diet cgroupfs_find_mountpoint() Namhyung Kim
2020-12-28  8:31   ` Jiri Olsa
2020-12-29  5:27     ` Namhyung Kim
2020-12-29  9:39       ` Jiri Olsa
2020-12-16  9:05 ` [PATCH 3/3] tools/lib/fs: Cache cgroupfs mount point Namhyung Kim
2020-12-29 11:51   ` Arnaldo Carvalho de Melo
2021-01-06  1:33     ` Namhyung Kim
2021-01-08  5:51       ` Namhyung Kim
2021-01-21  4:33         ` Namhyung Kim [this message]
2021-02-17 12:58         ` Arnaldo Carvalho de Melo
2021-02-19 10:05           ` Namhyung Kim
2021-02-19 11:37             ` Arnaldo Carvalho de Melo

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