From: Jan Kara <jack@suse.cz>
To: Oleg Nesterov <oleg@redhat.com>
Cc: peterz@infradead.org, Jan Kara <jack@suse.cz>,
Boaz Harrosh <boaz@plexistor.com>, Hou Tao <houtao1@huawei.com>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
Christoph Lameter <cl@linux.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count
Date: Fri, 18 Sep 2020 15:26:35 +0200 [thread overview]
Message-ID: <20200918132635.GI18920@quack2.suse.cz> (raw)
In-Reply-To: <20200918130914.GA26777@redhat.com>
On Fri 18-09-20 15:09:14, Oleg Nesterov wrote:
> On 09/18, Peter Zijlstra wrote:
> > > But again, do we really want this?
> >
> > I like the two counters better, avoids atomics entirely, some archs
> > hare horridly expensive atomics (*cough* power *cough*).
>
> I meant... do we really want to introduce percpu_up_read_irqsafe() ?
>
> Perhaps we can live with the fix from Hou? At least until we find a
> "real" performance regression.
I can say that for users of percpu rwsem in filesystems the cost of atomic
inc/dec is unlikely to matter. The lock hold times there are long enough
that it would be just lost in the noise.
For other stuff using them like get_online_cpus() or get_online_mems() I'm
not so sure...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-09-18 13:26 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 14:07 [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count Hou Tao
2020-09-15 15:06 ` peterz
2020-09-15 15:31 ` Oleg Nesterov
2020-09-15 15:51 ` peterz
2020-09-15 16:03 ` peterz
2020-09-15 16:11 ` Will Deacon
2020-09-15 18:11 ` peterz
2020-09-16 8:20 ` Will Deacon
2020-09-15 16:47 ` Oleg Nesterov
2020-09-16 12:32 ` Hou Tao
2020-09-16 12:51 ` peterz
2020-09-17 8:48 ` Will Deacon
2020-09-24 11:55 ` Hou Tao
2020-09-29 17:49 ` Will Deacon
2020-09-29 18:07 ` Ard Biesheuvel
2020-09-17 10:51 ` Boaz Harrosh
2020-09-17 12:01 ` Oleg Nesterov
2020-09-17 12:48 ` Matthew Wilcox
2020-09-17 13:22 ` peterz
2020-09-17 13:34 ` Oleg Nesterov
2020-09-17 13:46 ` Boaz Harrosh
2020-09-17 14:46 ` Christoph Hellwig
2020-09-18 9:07 ` Jan Kara
2020-09-18 10:01 ` peterz
2020-09-18 10:04 ` peterz
2020-09-18 10:07 ` peterz
2020-09-18 10:12 ` peterz
2020-09-18 10:48 ` Oleg Nesterov
2020-09-18 11:03 ` peterz
2020-09-18 13:09 ` Oleg Nesterov
2020-09-18 13:26 ` Jan Kara [this message]
2020-09-20 23:49 ` Dave Chinner
2020-09-18 8:36 ` [tip: locking/urgent] locking/percpu-rwsem: Use this_cpu_{inc,dec}() " tip-bot2 for Hou Tao
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