Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751259Ab3HKE57 (ORCPT ); Sun, 11 Aug 2013 00:57:59 -0400 Received: from terminus.zytor.com ([198.137.202.10]:38136 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750963Ab3HKE56 (ORCPT ); Sun, 11 Aug 2013 00:57:58 -0400 User-Agent: K-9 Mail for Android In-Reply-To: <1376195819.7006.18.camel@marge.simpson.net> References: <1376089460-5459-1-git-send-email-andi@firstfloor.org> <5205C4BB.6020003@zytor.com> <1376114128.5332.17.camel@marge.simpson.net> <5206659F.9070705@zytor.com> <1376194657.7006.11.camel@marge.simpson.net> <520712AE.6060904@zytor.com> <1376195819.7006.18.camel@marge.simpson.net> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: Re-tune x86 uaccess code for PREEMPT_VOLUNTARY From: "H. Peter Anvin" Date: Sat, 10 Aug 2013 21:57:26 -0700 To: Mike Galbraith CC: Andi Kleen , linux-kernel@vger.kernel.org, x86@kernel.org, mingo@kernel.org, torvalds@linux-foundation.org Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2056 Lines: 60 That sounds like an issue with specific preemption policies. Mike Galbraith wrote: >On Sat, 2013-08-10 at 21:27 -0700, H. Peter Anvin wrote: >> On 08/10/2013 09:17 PM, Mike Galbraith wrote: >> >> >> >> Do you have any quantification of "munches throughput?" It seems >odd >> >> that it would be worse than polling for preempt all over the >kernel, but >> >> perhaps the additional locking is what costs. >> > >> > I hadn't compared in ages, so made some fresh samples. >> > >> > Q6600 3.11-rc4 >> > >> > vmark >> > voluntary 169808 155826 154741 1.000 >> > preempt 149354 124016 128436 .836 >> > >> > That should be ~worst case, it hates preemption. >> > >> > tbench 8 >> > voluntary 1027.96 1028.76 1044.60 1.000 >> > preempt 929.06 935.01 928.64 .900 >> > >> > hackbench -l 10000 >> > voluntary 23.146 23.124 23.230 1.000 >> > preempt 25.065 24.633 24.789 1.071 >> > >> > kbuild vmlinux >> > voluntary 3m44.842s 3m42.975s 3m42.954s 1.000 >> > preempt 3m46.141s 3m45.835s 3m45.953s 1.010 >> > >> > Compute load comparisons are boring 'course. >> > >> >> I presume voluntary is indistinguishable from no preemption at all? > >No, all preemption options produce performance deltas. > >> Either way, that is definitely a reproducible test case, so if >someone >> is willing to take on optimizing preemption they can use vmark as the >> litmus test. It would be really awesome if we genuinely could get >the >> cost of preemption down to where it just doesn't matter. > >You have to eat more scheduler cycles, that's what PREEMPT does for a >living. Release a lock, wham. > >-Mike -- Sent from my mobile phone. Please excuse brevity and lack of formatting. -- 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/