From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org (Andrew Morton) Date: Tue, 3 Feb 2015 02:59:25 -0800 Subject: [RFC] change non-atomic bitops method 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> Message-ID: <20150203025925.d1c95fb8.akpm@linux-foundation.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 at 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.