Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759878AbbBIISR (ORCPT ); Mon, 9 Feb 2015 03:18:17 -0500 Received: from cnbjrel01.sonyericsson.com ([219.141.167.165]:17902 "EHLO cnbjrel01.sonyericsson.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759539AbbBIISO convert rfc822-to-8bit (ORCPT ); Mon, 9 Feb 2015 03:18:14 -0500 From: "Wang, Yalin" To: "'Andrew Morton'" CC: "'Kirill A. Shutemov'" , "'arnd@arndb.de'" , "'linux-arch@vger.kernel.org'" , "'linux-kernel@vger.kernel.org'" , "'linux@arm.linux.org.uk'" , "'linux-arm-kernel@lists.infradead.org'" Date: Mon, 9 Feb 2015 16:18:10 +0800 Subject: RE: [RFC] change non-atomic bitops method Thread-Topic: [RFC] change non-atomic bitops method Thread-Index: AdA/oIykaly/ngq4QxevAgovft523wEn53TQ Message-ID: <35FD53F367049845BC99AC72306C23D1044A02027E12@CNBJMBX05.corpusers.net> References: <35FD53F367049845BC99AC72306C23D1044A02027E0A@CNBJMBX05.corpusers.net> <20150202152909.13bfd11f192fb0268b2ab4bf@linux-foundation.org> <20150203011730.GA15653@node.dhcp.inet.fi> <35FD53F367049845BC99AC72306C23D1044A02027E0B@CNBJMBX05.corpusers.net> <35FD53F367049845BC99AC72306C23D1044A02027E0C@CNBJMBX05.corpusers.net> <20150202223851.f30768d0.akpm@linux-foundation.org> <35FD53F367049845BC99AC72306C23D1044A02027E0D@CNBJMBX05.corpusers.net> <35FD53F367049845BC99AC72306C23D1044A02027E0E@CNBJMBX05.corpusers.net> <20150203025925.d1c95fb8.akpm@linux-foundation.org> In-Reply-To: <20150203025925.d1c95fb8.akpm@linux-foundation.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3314 Lines: 88 > -----Original Message----- > From: Andrew Morton [mailto:akpm@linux-foundation.org] > Sent: Tuesday, February 03, 2015 6:59 PM > To: Wang, Yalin > Cc: 'Kirill A. Shutemov'; 'arnd@arndb.de'; 'linux-arch@vger.kernel.org'; > 'linux-kernel@vger.kernel.org'; 'linux@arm.linux.org.uk'; 'linux-arm- > kernel@lists.infradead.org' > Subject: Re: [RFC] change non-atomic bitops method > > On Tue, 3 Feb 2015 16:42:14 +0800 "Wang, Yalin" > wrote: > > > I make a change in kernel to test hit/miss ratio: > > Neat, thanks. > > > > > ... > > > > After use the phone some time: > > root@D5303:/ # cat /proc/meminfo > > VmallocUsed: 10348 kB > > VmallocChunk: 75632 kB > > __set_bit_miss_count:10002 __set_bit_success_count:1096661 > > __clear_bit_miss_count:359484 __clear_bit_success_count:3674617 > > __test_and_set_bit_miss_count:7 __test_and_set_bit_success_count:221 > > __test_and_clear_bit_miss_count:924611 > __test_and_clear_bit_success_count:193 > > > > __test_and_clear_bit_miss_count has a very high miss rate. > > In fact, I think set/clear/test_and_set(clear)_bit atomic version can > also > > Be investigated to see its miss ratio, > > I have not tested the atomic version, > > Because it reside in different architectures. > > Hopefully misses in test_and_X_bit are not a problem. The CPU > implementation would be pretty stupid to go and dirty the cacheline > when it knows it didn't change anything. But maybe I'm wrong about > that. > > That we're running clear_bit against a cleared bit 10% of the time is a > bit alarming. I wonder where that's coming from. > > The enormous miss count in test_and_clear_bit() might indicate an > inefficiency somewhere. I te-test the patch on 3.10 kernel. The result like this: VmallocChunk: 251498164 kB __set_bit_miss_count:11730 __set_bit_success_count:1036316 __clear_bit_miss_count:209640 __clear_bit_success_count:4806556 __test_and_set_bit_miss_count:0 __test_and_set_bit_success_count:121 __test_and_clear_bit_miss_count:0 __test_and_clear_bit_success_count:445 __clear_bit miss rate is a little high, I check the log, and most miss coming from this code: <6>[ 442.701798] [] warn_slowpath_fmt+0x4c/0x58 <6>[ 442.701805] [] __clear_bit+0x98/0xa4 <6>[ 442.701813] [] __alloc_fd+0xc8/0x124 <6>[ 442.701821] [] get_unused_fd_flags+0x28/0x34 <6>[ 442.701828] [] do_sys_open+0x10c/0x1c0 <6>[ 442.701835] [] SyS_openat+0xc/0x18 In __clear_close_on_exec(fd, fdt); <6>[ 442.695354] [] warn_slowpath_fmt+0x4c/0x58 <6>[ 442.695359] [] __clear_bit+0x98/0xa4 <6>[ 442.695367] [] dup_fd+0x1d4/0x280 <6>[ 442.695375] [] copy_process.part.56+0x42c/0xe38 <6>[ 442.695382] [] do_fork+0xe0/0x360 <6>[ 442.695389] [] SyS_clone+0x10/0x1c In __clear_open_fd(open_files - i, new_fdt); Do we need test_bit() before clear_bit()at these 2 place? Thanks -- 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/