All of lore.kernel.org
 help / color / mirror / Atom feed
From: Roman Gushchin <guro@fb.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Michal Hocko" <mhocko@kernel.org>,
	"Michal Koutný" <mkoutny@suse.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Vladimir Davydov" <vdavydov.dev@gmail.com>,
	"Waiman Long" <longman@redhat.com>,
	"Michal Hocko" <mhocko@suse.com>
Subject: Re: [PATCH v2 1/4] mm/memcg: Revert ("mm/memcg: optimize user context object stock access")
Date: Mon, 14 Feb 2022 11:45:23 -0800	[thread overview]
Message-ID: <YgqxUxM7SNX2QLuM@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <20220211223537.2175879-2-bigeasy@linutronix.de>

On Fri, Feb 11, 2022 at 11:35:34PM +0100, Sebastian Andrzej Siewior wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> The optimisation is based on a micro benchmark where local_irq_save() is
> more expensive than a preempt_disable(). There is no evidence that it is
> visible in a real-world workload and there are CPUs where the opposite is
> true (local_irq_save() is cheaper than preempt_disable()).
> 
> Based on micro benchmarks, the optimisation makes sense on PREEMPT_NONE
> where preempt_disable() is optimized away. There is no improvement with
> PREEMPT_DYNAMIC since the preemption counter is always available.
> 
> The optimization makes also the PREEMPT_RT integration more complicated
> since most of the assumption are not true on PREEMPT_RT.
> 
> Revert the optimisation since it complicates the PREEMPT_RT integration
> and the improvement is hardly visible.
> 
> [ bigeasy: Patch body around Michal's diff ]
> 
> Link: https://lore.kernel.org/all/YgOGkXXCrD%2F1k+p4@dhcp22.suse.cz
> Link: https://lkml.kernel.org/r/YdX+INO9gQje6d0S@linutronix.de
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Acked-by: Roman Gushchin <guro@fb.com>

Thanks!


WARNING: multiple messages have this Message-ID (diff)
From: Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>
To: Sebastian Andrzej Siewior
	<bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	"Andrew Morton"
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	"Johannes Weiner"
	<hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
	"Michal Hocko" <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	"Michal Koutný" <mkoutny-IBi9RG/b67k@public.gmane.org>,
	"Peter Zijlstra" <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	"Thomas Gleixner" <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	"Vladimir Davydov"
	<vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	"Waiman Long" <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"Michal Hocko" <mhocko-IBi9RG/b67k@public.gmane.org>
Subject: Re: [PATCH v2 1/4] mm/memcg: Revert ("mm/memcg: optimize user context object stock access")
Date: Mon, 14 Feb 2022 11:45:23 -0800	[thread overview]
Message-ID: <YgqxUxM7SNX2QLuM@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <20220211223537.2175879-2-bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>

On Fri, Feb 11, 2022 at 11:35:34PM +0100, Sebastian Andrzej Siewior wrote:
> From: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
> 
> The optimisation is based on a micro benchmark where local_irq_save() is
> more expensive than a preempt_disable(). There is no evidence that it is
> visible in a real-world workload and there are CPUs where the opposite is
> true (local_irq_save() is cheaper than preempt_disable()).
> 
> Based on micro benchmarks, the optimisation makes sense on PREEMPT_NONE
> where preempt_disable() is optimized away. There is no improvement with
> PREEMPT_DYNAMIC since the preemption counter is always available.
> 
> The optimization makes also the PREEMPT_RT integration more complicated
> since most of the assumption are not true on PREEMPT_RT.
> 
> Revert the optimisation since it complicates the PREEMPT_RT integration
> and the improvement is hardly visible.
> 
> [ bigeasy: Patch body around Michal's diff ]
> 
> Link: https://lore.kernel.org/all/YgOGkXXCrD%2F1k+p4-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org
> Link: https://lkml.kernel.org/r/YdX+INO9gQje6d0S-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org
> Signed-off-by: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>

Acked-by: Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>

Thanks!

  parent reply	other threads:[~2022-02-14 19:45 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-11 22:35 [PATCH v2 0/4] mm/memcg: Address PREEMPT_RT problems instead of disabling it Sebastian Andrzej Siewior
2022-02-11 22:35 ` Sebastian Andrzej Siewior
2022-02-11 22:35 ` [PATCH v2 1/4] mm/memcg: Revert ("mm/memcg: optimize user context object stock access") Sebastian Andrzej Siewior
2022-02-11 22:35   ` Sebastian Andrzej Siewior
2022-02-14 16:23   ` Johannes Weiner
2022-02-14 16:23     ` Johannes Weiner
2022-02-14 19:45   ` Roman Gushchin [this message]
2022-02-14 19:45     ` Roman Gushchin
2022-02-11 22:35 ` [PATCH v2 2/4] mm/memcg: Disable threshold event handlers on PREEMPT_RT Sebastian Andrzej Siewior
2022-02-11 22:35   ` Sebastian Andrzej Siewior
2022-02-14 16:23   ` Johannes Weiner
2022-02-14 16:23     ` Johannes Weiner
2022-02-14 19:46   ` Roman Gushchin
2022-02-14 19:46     ` Roman Gushchin
2022-02-11 22:35 ` [PATCH v2 3/4] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT where needed Sebastian Andrzej Siewior
2022-02-11 22:35   ` Sebastian Andrzej Siewior
2022-02-14 16:46   ` Johannes Weiner
2022-02-14 16:46     ` Johannes Weiner
2022-02-14 19:53     ` Roman Gushchin
2022-02-14 19:53       ` Roman Gushchin
2022-02-15 18:01     ` Sebastian Andrzej Siewior
2022-02-15 18:01       ` Sebastian Andrzej Siewior
2022-02-11 22:35 ` [PATCH v2 4/4] mm/memcg: Protect memcg_stock with a local_lock_t Sebastian Andrzej Siewior
2022-02-11 22:35   ` Sebastian Andrzej Siewior
2022-02-14 16:23   ` Johannes Weiner
2022-02-14 16:23     ` Johannes Weiner
2022-02-16 15:51     ` Sebastian Andrzej Siewior
2022-02-16 15:51       ` Sebastian Andrzej Siewior
2022-02-16 18:08       ` Johannes Weiner
2022-02-16 18:08         ` Johannes Weiner
2022-02-17  9:28         ` Sebastian Andrzej Siewior
2022-02-17  9:28           ` Sebastian Andrzej Siewior
2022-02-12 10:39 [PATCH v2 1/4] mm/memcg: Revert ("mm/memcg: optimize user context object stock access") kernel test robot

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=YgqxUxM7SNX2QLuM@carbon.dhcp.thefacebook.com \
    --to=guro@fb.com \
    --cc=akpm@linux-foundation.org \
    --cc=bigeasy@linutronix.de \
    --cc=cgroups@vger.kernel.org \
    --cc=hannes@cmpxchg.org \
    --cc=linux-mm@kvack.org \
    --cc=longman@redhat.com \
    --cc=mhocko@kernel.org \
    --cc=mhocko@suse.com \
    --cc=mkoutny@suse.com \
    --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 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.