From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK Date: Fri, 21 Feb 2014 18:01:29 -0500 Message-ID: <5307DAC9.2020103@hurleysoftware.com> References: <1392929071-16555-5-git-send-email-tj@kernel.org> <5306AF8E.3080006@hurleysoftware.com> <20140221015935.GF6897@htj.dyndns.org> <5306B4DF.4000901@hurleysoftware.com> <20140221021341.GG6897@htj.dyndns.org> <5306E06C.5020805@hurleysoftware.com> <20140221100301.GA14653@mtj.dyndns.org> <53074BE4.1020307@hurleysoftware.com> <20140221130614.GH6897@htj.dyndns.org> <5307849A.9050209@hurleysoftware.com> <20140221165730.GA10929@htj.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140221165730.GA10929@htj.dyndns.org> Sender: linux-kernel-owner@vger.kernel.org To: Tejun Heo Cc: laijs@cn.fujitsu.com, linux-kernel@vger.kernel.org, Stefan Richter , linux1394-devel@lists.sourceforge.net, Chris Boot , linux-scsi@vger.kernel.org, target-devel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org On 02/21/2014 11:57 AM, Tejun Heo wrote: > Yo, > > On Fri, Feb 21, 2014 at 11:53:46AM -0500, Peter Hurley wrote: >> Ok, I can do that. But AFAIK it'll have to be an smp_rmb(); there is >> no mb__after unlock. > > We do have smp_mb__after_unlock_lock(). > >> [ After thinking about it some, I don't think preventing speculative >> writes before clearing PENDING if useful or necessary, so that's >> why I'm suggesting only the rmb. ] > > But smp_mb__after_unlock_lock() would be cheaper on most popular > archs, I think. smp_mb__after_unlock_lock() is only for ordering memory operations between two spin-locked sections on either the same lock or by the same task/cpu. Like: i = 1 spin_unlock(lock1) spin_lock(lock2) smp_mb__after_unlock_lock() j = 1 This guarantees that the store to j happens after the store to i. Without it, a cpu can spin_lock(lock2) j = 1 i = 1 spin_unlock(lock1) Regards, Peter Hurley