Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751820AbbD3VVQ (ORCPT ); Thu, 30 Apr 2015 17:21:16 -0400 Received: from g2t2352.austin.hp.com ([15.217.128.51]:34968 "EHLO g2t2352.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751023AbbD3VVN (ORCPT ); Thu, 30 Apr 2015 17:21:13 -0400 Message-ID: <1430428872.2475.51.camel@j-VirtualBox> Subject: Re: [PATCH v4 1/2] locking/rwsem: reduce spinlock contention in wakeup after up_read/up_write From: Jason Low To: Waiman Long Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Davidlohr Bueso , Scott J Norton , Douglas Hatch , jason.low2@hp.com Date: Thu, 30 Apr 2015 14:21:12 -0700 In-Reply-To: <1430428337-16802-2-git-send-email-Waiman.Long@hp.com> References: <1430428337-16802-1-git-send-email-Waiman.Long@hp.com> <1430428337-16802-2-git-send-email-Waiman.Long@hp.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1271 Lines: 26 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 > Suggested-by: Peter Zijlstra (Intel) Acked-by: Jason Low -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/