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From: Sebastian Andrzej Siewior <bigeasy-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
To: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
	Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Vladimir Davydov
	<vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
Subject: Re: [PATCH-next v3] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT
Date: Fri, 17 Dec 2021 20:48:47 +0100	[thread overview]
Message-ID: <Ybzpn59+ecDCnULt@linutronix.de> (raw)
In-Reply-To: <b82efbad-1eb2-9441-ab0b-cbb3d2b5eac6-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

On 2021-12-17 13:46:53 [-0500], Waiman Long wrote:
> > annotation. Looking at the history, I'm also impressed by that fact that
> > disabling/ enabling interrupts is *so* expensive that all this is
> > actually worth it.
> 
> For !RT with voluntary or no preemption, preempt_disable() is just a
> compiler barrier. So it is definitely cheaper than disabling interrupt. The
> performance benefit is less with preemptible but !RT kernel. Microbenchmark
> testing shows a performance improvement of a few percents depending on the
> exact benchmark.

Thanks for confirming. I got the feeling that this optimisation is for
!CONFIG_PREEMPTION. So I instead of depending on CONFIG_PREEMPT_RT I'm
leaning towards CONFIG_PREEMPT instead.

> Cheers,
> Longman

Sebastian

WARNING: multiple messages have this Message-ID (diff)
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Waiman Long <longman@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH-next v3] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT
Date: Fri, 17 Dec 2021 20:48:47 +0100	[thread overview]
Message-ID: <Ybzpn59+ecDCnULt@linutronix.de> (raw)
In-Reply-To: <b82efbad-1eb2-9441-ab0b-cbb3d2b5eac6@redhat.com>

On 2021-12-17 13:46:53 [-0500], Waiman Long wrote:
> > annotation. Looking at the history, I'm also impressed by that fact that
> > disabling/ enabling interrupts is *so* expensive that all this is
> > actually worth it.
> 
> For !RT with voluntary or no preemption, preempt_disable() is just a
> compiler barrier. So it is definitely cheaper than disabling interrupt. The
> performance benefit is less with preemptible but !RT kernel. Microbenchmark
> testing shows a performance improvement of a few percents depending on the
> exact benchmark.

Thanks for confirming. I got the feeling that this optimisation is for
!CONFIG_PREEMPTION. So I instead of depending on CONFIG_PREEMPT_RT I'm
leaning towards CONFIG_PREEMPT instead.

> Cheers,
> Longman

Sebastian


  parent reply	other threads:[~2021-12-17 19:48 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-14 14:44 [PATCH-next v3] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT Waiman Long
     [not found] ` <20211214144412.447035-1-longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2021-12-15  4:36   ` Davidlohr Bueso
2021-12-15  4:36     ` Davidlohr Bueso
2021-12-15 16:58     ` Waiman Long
2021-12-15 16:58       ` Waiman Long
2021-12-17 11:42   ` Sebastian Andrzej Siewior
2021-12-17 11:42     ` Sebastian Andrzej Siewior
     [not found]     ` <Ybx3ubNFfGpCqhn0-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
2021-12-17 18:21       ` Sebastian Andrzej Siewior
2021-12-17 18:21         ` Sebastian Andrzej Siewior
2021-12-17 18:46       ` Waiman Long
2021-12-17 18:46         ` Waiman Long
     [not found]         ` <b82efbad-1eb2-9441-ab0b-cbb3d2b5eac6-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2021-12-17 19:48           ` Sebastian Andrzej Siewior [this message]
2021-12-17 19:48             ` Sebastian Andrzej Siewior
2021-12-19 13:20 ` [mm/memcg] 3928ba024a: WARNING:possible_recursive_locking_detected kernel test robot
2021-12-19 13:20   ` kernel test robot

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