From: Kees Cook <keescook@chromium.org>
To: Mateusz Guzik <mjguzik@gmail.com>
Cc: Kees Cook <kees@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Eric Biederman <ebiederm@xmission.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs/exec.c: Add fast path for ENOENT on PATH search before allocating mm
Date: Wed, 8 Nov 2023 11:25:34 -0800 [thread overview]
Message-ID: <202311081123.391A316@keescook> (raw)
In-Reply-To: <CAGudoHESNDTAAOGB3riYjU3tgHTXVLRdB7tknfVBem38yqkJEA@mail.gmail.com>
On Wed, Nov 08, 2023 at 01:03:33AM +0100, Mateusz Guzik wrote:
> [...]
> >>@[
> >> __pv_queued_spin_lock_slowpath+1
> >> _raw_spin_lock_irq+43
> >> wait_for_completion+141
> >> stop_one_cpu+127
> >> sched_exec+165
> >
> > There's the suspicious sched_exec() I was talking about! :)
> >
> > I think it needs to be moved, and perhaps _later_ instead of earlier?
> > Hmm...
> >
>
> I'm getting around 3.4k execs/s. However, if I "taskset -c 3
> ./static-doexec 1" the number goes up to about 9.5k and lock
> contention disappears from the profile. So off hand looks like the
> task is walking around the box when it perhaps could be avoided -- it
> is idle apart from running the test. Again this is going to require a
> serious look instead of ad hoc pokes.
Hm, that is pretty interesting. I'll see if I can go find the original
rationale for adding sched_exec() in there...
> Side note I actually read your patch this time around instead of
> skimming through it and assuming it did what I thought.
>
> do_filp_open is of course very expensive and kmalloc + kfree are slow.
> On top of it deallocating a file object even after a failed open was
> very expensive due to delegation to task_work (recently fixed).
>
> What I claim should be clear-cut faster is that lookup as in the
> original patch and only messing with file allocation et al if it
> succeeds.
I'm less familiar with the VFS guts here -- I'm open to alternatives! :)
--
Kees Cook
next prev parent reply other threads:[~2023-11-08 19:25 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-16 13:41 [PATCH] fs/exec.c: Add fast path for ENOENT on PATH search before allocating mm Josh Triplett
2022-09-16 14:38 ` Kees Cook
2022-09-16 20:13 ` Josh Triplett
2022-09-17 0:11 ` Kees Cook
2022-09-17 0:50 ` Josh Triplett
2022-09-19 20:02 ` Kees Cook
2022-10-01 16:01 ` Josh Triplett
2022-09-19 14:34 ` Peter Zijlstra
2022-09-22 7:27 ` [fs/exec.c] 0a276ae2d2: BUG:workqueue_lockup-pool kernel test robot
2023-11-07 20:30 ` [PATCH] fs/exec.c: Add fast path for ENOENT on PATH search before allocating mm Kees Cook
2023-11-07 20:51 ` Mateusz Guzik
2023-11-07 21:23 ` Mateusz Guzik
2023-11-07 22:50 ` Kees Cook
2023-11-07 23:08 ` Mateusz Guzik
2023-11-07 23:39 ` Kees Cook
2023-11-08 0:03 ` Mateusz Guzik
2023-11-08 19:25 ` Kees Cook [this message]
2023-11-08 19:31 ` Kees Cook
2023-11-08 19:35 ` Mateusz Guzik
2023-11-09 0:17 ` Eric W. Biederman
2023-11-09 12:21 ` Mateusz Guzik
2023-11-10 5:26 ` Eric W. Biederman
2023-11-07 20:37 ` Kees Cook
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