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From: Davidlohr Bueso <dave@stgolabs.net>
To: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] locking/rwsem: Make owner store task pointer of last owning reader
Date: Mon, 10 Sep 2018 10:15:50 -0700	[thread overview]
Message-ID: <20180910171550.GA3902@linux-r8p5> (raw)
In-Reply-To: <83b333ea-8ef2-84ea-6810-4ab1a67eef88@redhat.com>

On Mon, 10 Sep 2018, Waiman Long wrote:

>One major issue with a combined count/owner is that we may have to use
>cmpxchg for reader lock which will certainly impact reader-heavy
>workloads. I have also thought about ways to compress the task pointer
>address so that it can use fewer bits and leave the rests for reader
>count. It is probably doable on 64-bit systems, but likely not on 32-bit
>system given that there are less bits to play around.

Yeah we've discussed this before. As a cleanup it would obviously be good,
but I fear about raw performance loss when using cmpxchg instead of xadd.

Thanks,
Davidlohr

  reply	other threads:[~2018-09-10 17:16 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-06 20:18 [PATCH] locking/rwsem: Make owner store task pointer of last owning reader Waiman Long
2018-09-10  9:31 ` Peter Zijlstra
2018-09-10 15:01   ` Waiman Long
2018-09-10 17:15     ` Davidlohr Bueso [this message]
2018-09-10 17:35       ` Waiman Long
2018-09-11  8:17       ` Peter Zijlstra
2018-09-11 12:56         ` Waiman Long
2018-09-11 19:21   ` Davidlohr Bueso
2018-09-11 19:38     ` Peter Zijlstra
2018-09-10 10:54 ` [tip:locking/core] " tip-bot for Waiman Long

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