From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [REPOST] RFC: sched: Prevent wakeup to enter critical section needlessly Date: Tue, 09 Oct 2012 06:37:27 -0700 Message-ID: References: <1348491997-30898-1-git-send-email-meltedpianoman@gmail.com> <1349782235-8896-1-git-send-email-meltedpianoman@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mga09.intel.com ([134.134.136.24]:61262 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755655Ab2JINhb (ORCPT ); Tue, 9 Oct 2012 09:37:31 -0400 In-Reply-To: <1349782235-8896-1-git-send-email-meltedpianoman@gmail.com> (Ivo Sieben's message of "Tue, 9 Oct 2012 13:30:35 +0200") Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Ivo Sieben Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , linux-serial@vger.kernel.org, Alan Cox , Greg KH Ivo Sieben writes: > Check the waitqueue task list to be non empty before entering the critical > section. This prevents locking the spin lock needlessly in case the queue > was empty, and therefor also prevent scheduling overhead on a PREEMPT_RT > system. > > Signed-off-by: Ivo Sieben > --- > > REPOST: > Request for comments: > - Does this make any sense? Looks good to me. Avoiding any spinlock is good. I don't even think you need "careful", if you miss an update it was just as it happened a little later. -Andi -- ak@linux.intel.com -- Speaking for myself only