Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755752AbbBCK7y (ORCPT ); Tue, 3 Feb 2015 05:59:54 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:42831 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754587AbbBCK7w (ORCPT ); Tue, 3 Feb 2015 05:59:52 -0500 Date: Tue, 3 Feb 2015 02:59:25 -0800 From: Andrew Morton 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 Message-Id: <20150203025925.d1c95fb8.akpm@linux-foundation.org> In-Reply-To: <35FD53F367049845BC99AC72306C23D1044A02027E0E@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> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1505 Lines: 39 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. -- 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/