All of lore.kernel.org
 help / color / mirror / Atom feed
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAM9d7ci5W06UNthEBBs=-wJLjusO=bpFg2sFj=M0W3h20+oaHA@mail.gmail.com' \
    --to=namhyung@kernel.org \
    --cc=acme@kernel.org \
    --cc=ak@linux.intel.com \
    --cc=alexander.shishkin@linux.intel.com \
    --cc=eranian@google.com \
    --cc=irogers@google.com \
    --cc=jolsa@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.