From: Johannes Weiner <hannes@cmpxchg.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
"Andrew Morton" <akpm@linux-foundation.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 11:23:33 -0500 [thread overview]
Message-ID: <YgqCBU4mVwkgnBi2@cmpxchg.org> (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: Johannes Weiner <hannes@cmpxchg.org>
next prev parent reply other threads:[~2022-02-14 16:23 UTC|newest]
Thread overview: 16+ 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 ` [PATCH v2 1/4] mm/memcg: Revert ("mm/memcg: optimize user context object stock access") Sebastian Andrzej Siewior
2022-02-14 16:23 ` Johannes Weiner [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
2022-02-14 16:23 ` Johannes Weiner
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
2022-02-14 16:46 ` Johannes Weiner
2022-02-14 19:53 ` Roman Gushchin
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
2022-02-14 16:23 ` Johannes Weiner
2022-02-16 15:51 ` Sebastian Andrzej Siewior
2022-02-16 18:08 ` Johannes Weiner
2022-02-17 9:28 ` Sebastian Andrzej Siewior
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