Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967097Ab3DROeb (ORCPT ); Thu, 18 Apr 2013 10:34:31 -0400 Received: from mga09.intel.com ([134.134.136.24]:46954 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966791Ab3DROea (ORCPT ); Thu, 18 Apr 2013 10:34:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,502,1363158000"; d="scan'208";a="296957639" Message-ID: <51700475.7050102@linux.intel.com> Date: Thu, 18 Apr 2013 07:34:29 -0700 From: Darren Hart User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: zhang.yi20@zte.com.cn CC: Dave Hansen , Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar , Peter Zijlstra , Thomas Gleixner Subject: Re: [PATCH] futex: bugfix for futex-key conflict when futex use hugepage References: <516EAF31.8000107@linux.intel.com> <516EBF23.2090600@sr71.net> <516EC508.6070200@linux.intel.com> In-Reply-To: X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3554 Lines: 100 On 04/18/2013 01:05 AM, zhang.yi20@zte.com.cn wrote: > Darren Hart wrote on 2013/04/17 23:51:36: > >> On 04/17/2013 08:26 AM, Dave Hansen wrote: >>> On 04/17/2013 07:18 AM, Darren Hart wrote: >>>>>> This also needs a comment in futex.h describing the usage of the >>>>>> offset field in union futex_key as well as above get_futex_key >>>>>> describing the key for shared mappings. >>>>>> >>>>> As far as I know , the max size of one hugepage is 1 GBytes for >>>>> x86 cpu. Can some other cpus support greater hugepage even more >>>>> than 4 GBytes? If so, we can change the type of 'offset' from int >>>>> to long to avoid truncating. >>>> >>>> I discussed this with Dave Hansen, on CC, and he thought we needed >>>> 9 bits, so even on x86 32b we should be covered. >>> >>> I think the problem is actually on 64-bit since you still only have >>> 32-bits in an 'int' there. >>> >>> I guess it's remotely possible that we could have some >>> mega-super-huge-gigantic pages show up in hardware some day, or that >>> somebody would come up with software-only one. I bet there's a lot >>> more code that will break in the kernel than this futex code, though. >>> >>> The other option would be to start #defining some build-time constant >>> for what the largest possible huge page size is, then BUILD_BUG_ON() >>> it. >>> >>> Or you can just make it a long ;) >> >> If we make it a long I'd want to see futextest performance tests before >> and after. Messing with the futex_key has been known to have bad results >> in the past :-) >> >> -- > > I have run futextest/performance/futex_wait for testing, 5 times before > make it long: > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 10215 Kiter/s > > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 9862 Kiter/s > > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 10081 Kiter/s > > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 10060 Kiter/s > > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 10081 Kiter/s > > > And 5 times after make it long: > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 9940 Kiter/s > > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 10204 Kiter/s > > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 9901 Kiter/s > > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 10152 Kiter/s > > futex_wait: Measure FUTEX_WAIT operations per second > Arguments: iterations=100000000 threads=256 > Result: 10060 Kiter/s > > > Seems OK, is it? > Changes appear to be in the noise, no impact with this load anyway. How many CPUs on your test machine? I presume not 256? -- Darren Hart Intel Open Source Technology Center Yocto Project - Technical Lead - Linux Kernel -- 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/