From: Jason Low <jason.low2@hp.com>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org, Davidlohr Bueso <dave@stgolabs.net>,
Scott J Norton <scott.norton@hp.com>,
Douglas Hatch <doug.hatch@hp.com>,
jason.low2@hp.com
Subject: Re: [PATCH v4 1/2] locking/rwsem: reduce spinlock contention in wakeup after up_read/up_write
Date: Thu, 30 Apr 2015 14:21:12 -0700 [thread overview]
Message-ID: <1430428872.2475.51.camel@j-VirtualBox> (raw)
In-Reply-To: <1430428337-16802-2-git-send-email-Waiman.Long@hp.com>
On Thu, 2015-04-30 at 17:12 -0400, Waiman Long wrote:
> In up_write()/up_read(), rwsem_wake() will be called whenever it
> detects that some writers/readers are waiting. The rwsem_wake()
> function will take the wait_lock and call __rwsem_do_wake() to do the
> real wakeup. For a heavily contended rwsem, doing a spin_lock() on
> wait_lock will cause further contention on the heavily contended rwsem
> cacheline resulting in delay in the completion of the up_read/up_write
> operations.
>
> This patch makes the wait_lock taking and the call to __rwsem_do_wake()
> optional if at least one spinning writer is present. The spinning
> writer will be able to take the rwsem and call rwsem_wake() later
> when it calls up_write(). With the presence of a spinning writer,
> rwsem_wake() will now try to acquire the lock using trylock. If that
> fails, it will just quit.
>
> Signed-off-by: Waiman Long <Waiman.Long@hp.com>
> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Jason Low <jason.low2@hp.com>
next prev parent reply other threads:[~2015-04-30 21:21 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-30 21:12 [PATCH v4 0/2] locking/rwsem: optimize rwsem_wakeup() Waiman Long
2015-04-30 21:12 ` [PATCH v4 1/2] locking/rwsem: reduce spinlock contention in wakeup after up_read/up_write Waiman Long
2015-04-30 21:21 ` Jason Low [this message]
2015-05-01 10:14 ` Peter Zijlstra
2015-05-06 11:18 ` Davidlohr Bueso
2015-05-06 11:20 ` Davidlohr Bueso
2015-05-08 13:24 ` [tip:locking/core] locking/rwsem: Reduce spinlock contention in wakeup after up_read()/up_write() tip-bot for Waiman Long
2015-04-30 21:12 ` [PATCH v4 2/2] locking/rwsem: check for active writer before wakeup Waiman Long
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