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From: peterz@infradead.org
To: Oleg Nesterov <oleg@redhat.com>
Cc: 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 13:03:10 +0200	[thread overview]
Message-ID: <20200918110310.GO1362448@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200918104824.GA23469@redhat.com>

On Fri, Sep 18, 2020 at 12:48:24PM +0200, Oleg Nesterov wrote:

> Of course, this assumes that atomic_t->counter underflows "correctly", just
> like "unsigned int".

We're documented that we do. Lots of code relies on that.

See Documentation/atomic_t.txt TYPES

> 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 just tried to be clever and use a single u64 load (where possible)
instead of two 32bit loads and got the sum vs split order wrong.

  reply	other threads:[~2020-09-18 11:03 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 14:07 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 [this message]
2020-09-18 13:09                         ` Oleg Nesterov
2020-09-18 13:26                           ` Jan Kara
2020-09-20 23:49                             ` Dave Chinner

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