From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758222Ab3FMCJd (ORCPT ); Wed, 12 Jun 2013 22:09:33 -0400 Received: from intranet.asianux.com ([58.214.24.6]:34332 "EHLO intranet.asianux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756400Ab3FMCJc (ORCPT ); Wed, 12 Jun 2013 22:09:32 -0400 X-Spam-Score: -100.8 Message-ID: <51B929AB.3040201@asianux.com> Date: Thu, 13 Jun 2013 10:08:43 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: Frederic Weisbecker , Thomas Gleixner , Sedat Dilek , Andrew Morton , Linus Torvalds , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] kernel/softirq.c: delete 'while' looping to improve a little performance and beautify code References: <51B4755B.4020205@asianux.com> <20130610122543.GG5146@linux.vnet.ibm.com> In-Reply-To: <20130610122543.GG5146@linux.vnet.ibm.com> Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/10/2013 08:25 PM, Paul E. McKenney wrote: > On Sun, Jun 09, 2013 at 08:30:19PM +0800, Chen Gang wrote: >> > >> > After finish the internal 'while', need not test TASKLET_STATE_SCHED >> > again, so looping back to outside 'while' is only for set_bit(). >> > >> > When use 'if' and set_bit() instead of 'while', it will save at least >> > one running conditional instruction, and also will be clearer for readers >> > (although the binary size will be a little bigger). >> > >> > The related patch is "1da177e Linux-2.6.12-rc2" >> > >> > >> > Signed-off-by: Chen Gang >> > --- >> > kernel/softirq.c | 3 ++- >> > 1 files changed, 2 insertions(+), 1 deletions(-) >> > >> > diff --git a/kernel/softirq.c b/kernel/softirq.c >> > index a5f8836..52da25f 100644 >> > --- a/kernel/softirq.c >> > +++ b/kernel/softirq.c >> > @@ -540,10 +540,11 @@ void tasklet_kill(struct tasklet_struct *t) >> > if (in_interrupt()) >> > printk("Attempt to kill tasklet from interrupt\n"); >> > >> > - while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) { >> > + if (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) { >> > do { >> > yield(); >> > } while (test_bit(TASKLET_STATE_SCHED, &t->state)); >> > + set_bit(TASKLET_STATE_SCHED, &t->state); > This replaces an atomic test-and-set with two operations, a test and > a set. Is this safe? Oh, it seems not safe, at least it is not the original author's willing. It is my fault, and also sorry for replying late. Thanks. -- Chen Gang Asianux Corporation