From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Waiman Long <longman@redhat.com>
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH 3/3] mm/memcg: Allow the task_obj optimization only on non-PREEMPTIBLE kernels.
Date: Thu, 13 Jan 2022 16:26:53 +0100 [thread overview]
Message-ID: <YeBEvaggZ7/6y5ij@linutronix.de> (raw)
In-Reply-To: <29457251-cf4f-4c7d-b36d-c2a0af4da707@redhat.com>
On 2022-01-05 22:28:10 [-0500], Waiman Long wrote:
> Thanks for the extensive testing. I usually perform my performance test on
> Intel hardware. I don't realize that Zen2 and arm64 perform better with irq
> on/off.
Maybe you have access to more recent µArch from Intel which could behave
different.
> My own testing when tracking the number of times in_task() is true or false
> indicated most of the kmalloc() call is done by tasks. Only a few percents
> of the time is in_task() false. That is the reason why I optimize the case
> that in_task() is true.
Right. This relies on the fact that changing preemption is cheaper which
is not always true. The ultimate benefit is of course when the
preemption changes can be removed/ optimized away.
> > Based on that, I don't see any added value by the optimisation once
> > PREEMPT_DYNAMIC is enabled.
>
> The PREEMPT_DYNAMIC result is a bit surprising to me. Given the data points,
> I am not going to object to this patch then. I will try to look further into
> why this is the case when I have time.
Okay, thank you.
In the SERVER case we keep the preemption counter so this has obviously
an impact. I am a little surprised that the DYN-FULL and DYN-NONE
differ a little since the code runs with disabled interrupts. But then
this might be the extra jump to preempt_schedule() which is patched-out
in the SERVER case.
> Cheers,
> Longman
Sebastian
next prev parent reply other threads:[~2022-01-13 15:26 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-22 11:41 [RFC PATCH 0/3] mm/memcg: Address PREEMPT_RT problems instead of disabling it Sebastian Andrzej Siewior
2021-12-22 11:41 ` [RFC PATCH 1/3] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT Sebastian Andrzej Siewior
2021-12-23 2:31 ` Waiman Long
2021-12-23 7:34 ` Sebastian Andrzej Siewior
2021-12-23 16:01 ` Waiman Long
2022-01-05 14:16 ` Michal Koutný
2022-01-13 13:08 ` Sebastian Andrzej Siewior
2022-01-13 14:48 ` Michal Koutný
2022-01-14 9:09 ` Sebastian Andrzej Siewior
2022-01-18 18:26 ` [PATCH] mm/memcg: Do not check v1 event counter when not needed Michal Koutný
2022-01-18 19:57 ` Sebastian Andrzej Siewior
2021-12-22 11:41 ` [RFC PATCH 2/3] mm/memcg: Add a local_lock_t for IRQ and TASK object Sebastian Andrzej Siewior
2021-12-23 21:38 ` Waiman Long
2022-01-03 16:34 ` Sebastian Andrzej Siewior
2022-01-03 17:09 ` Waiman Long
2021-12-22 11:41 ` [RFC PATCH 3/3] mm/memcg: Allow the task_obj optimization only on non-PREEMPTIBLE kernels Sebastian Andrzej Siewior
2021-12-23 21:48 ` Waiman Long
2022-01-03 14:44 ` Sebastian Andrzej Siewior
2022-01-03 15:04 ` Waiman Long
2022-01-05 20:22 ` Sebastian Andrzej Siewior
2022-01-06 3:28 ` Waiman Long
2022-01-13 15:26 ` Sebastian Andrzej Siewior [this message]
2022-01-05 14:59 ` [RFC PATCH 0/3] mm/memcg: Address PREEMPT_RT problems instead of disabling it Michal Koutný
2022-01-05 15:06 ` Sebastian Andrzej Siewior
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=YeBEvaggZ7/6y5ij@linutronix.de \
--to=bigeasy@linutronix.de \
--cc=akpm@linux-foundation.org \
--cc=cgroups@vger.kernel.org \
--cc=hannes@cmpxchg.org \
--cc=linux-mm@kvack.org \
--cc=longman@redhat.com \
--cc=mhocko@kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=vdavydov.dev@gmail.com \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).