Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030323AbVLVVph (ORCPT ); Thu, 22 Dec 2005 16:45:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030317AbVLVVph (ORCPT ); Thu, 22 Dec 2005 16:45:37 -0500 Received: from prgy-npn2.prodigy.com ([207.115.54.38]:32064 "EHLO oddball.prodigy.com") by vger.kernel.org with ESMTP id S1030323AbVLVVpg (ORCPT ); Thu, 22 Dec 2005 16:45:36 -0500 Message-ID: <43AB1E64.6010504@tmr.com> Date: Thu, 22 Dec 2005 16:45:08 -0500 From: Bill Davidsen User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050920 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Lee Revell CC: Zwane Mwaikambo , "Luck, Tony" , Tony Luck , Andrew Morton , linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, Jack Steiner , Keith Owens , Dimitri Sivanich Subject: Re: [PATCH] ia64: disable preemption in udelay() References: <20051214232526.9039.15753.sendpatchset@tomahawk.engr.sgi.com> <20051215225040.GA9086@agluck-lia64.sc.intel.com> <1134698636.12086.222.camel@mindpipe> <00b201c601e6$30c87ff0$d6069aa3@johnhaonw7lw1r> <1134703152.12086.231.camel@mindpipe> In-Reply-To: <1134703152.12086.231.camel@mindpipe> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1389 Lines: 34 Lee Revell wrote: > On Thu, 2005-12-15 at 18:12 -0800, John Hawkes wrote: > >>From: "Lee Revell" >> >>>There are 10 drivers that udelay(10000) or more and a TON that >>>udelay(1000). Turning those all into 1ms+ non preemptible sections will >>>be very bad. >> >>What about 100usec non-preemptible sections? > > > That will disappear into the noise, in normal usage these happen all the > time. 500usec non preemptible regions are rare (~1 hour to show up) and > 1ms very rare (24 hours). My tests show that 300 usec or so is a good > place to draw the line if you don't want it to show up in latency tests. I may be misreading the original post, but the problem is described as one where the TSC is not syncronised and a CPU switch takes place. Would the correct solution be to somehow set CPU affinity temporarily in such a way as to avoid disabling preempt at all? The preempt doesn't seem to be the root problem, so it's unlikely to be the best solution... -- -bill davidsen (davidsen@tmr.com) "The secret to procrastination is to put things off until the last possible moment - but no longer" -me - 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/