From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Ingo Molnar <mingo@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
Scott J Norton <scott.norton@hp.com>,
Douglas Hatch <doug.hatch@hp.com>
Subject: Re: [PATCH 2/2] locking/qrwlock: Don't contend with readers when setting _QW_WAITING
Date: Tue, 9 Jun 2015 14:04:20 +0200 [thread overview]
Message-ID: <20150609120420.GV3644@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1433802045-21298-3-git-send-email-Waiman.Long@hp.com>
On Mon, Jun 08, 2015 at 06:20:44PM -0400, Waiman Long wrote:
> The current cmpxchg() loop in setting the _QW_WAITING flag for writers
> in queue_write_lock_slowpath() will contend with incoming readers
> causing possibly extra cmpxchg() operations that are wasteful. This
> patch changes the code to do a byte cmpxchg() to eliminate contention
> with new readers.
This is very narrow, would not the main cost still be the cacheline
transfers?
Do you have any numbers to back this? I would feel much better about
this if there's real numbers attached.
next prev parent reply other threads:[~2015-06-09 12:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-08 22:20 [PATCH 0/2] locking/qrwlock: Fix interrupt handling problem Waiman Long
2015-06-08 22:20 ` [PATCH 1/2] locking/qrwlock: Fix bug in interrupt handling code Waiman Long
2015-06-08 22:20 ` [PATCH 2/2] locking/qrwlock: Don't contend with readers when setting _QW_WAITING Waiman Long
2015-06-09 12:04 ` Peter Zijlstra [this message]
2015-06-09 15:23 ` Waiman Long
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