> -----Original Message----- > From: Andrew Morton [mailto:akpm@xxxxxxxxxxxxxxxxxxxx] > Sent: Tuesday, February 03, 2015 6:59 PM > To: Wang, Yalin > Cc: 'Kirill A. Shutemov'; 'arnd@xxxxxxxx'; 'linux-arch@xxxxxxxxxxxxxxx'; > 'linux-kernel@xxxxxxxxxxxxxxx'; 'linux@xxxxxxxxxxxxxxxx'; 'linux-arm- > kernel@xxxxxxxxxxxxxxxxxxx' > Subject: Re: [RFC] change non-atomic bitops method > > On Tue, 3 Feb 2015 16:42:14 +0800 "Wang, Yalin" <Yalin.Wang@xxxxxxxxxxxxxx> > 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] [<ffffffc00021d084>] warn_slowpath_fmt+0x4c/0x58 <6>[ 442.701805] [<ffffffc0002461a8>] __clear_bit+0x98/0xa4 <6>[ 442.701813] [<ffffffc0003126ac>] __alloc_fd+0xc8/0x124 <6>[ 442.701821] [<ffffffc000312768>] get_unused_fd_flags+0x28/0x34 <6>[ 442.701828] [<ffffffc0002f9370>] do_sys_open+0x10c/0x1c0 <6>[ 442.701835] [<ffffffc0002f9458>] SyS_openat+0xc/0x18 In __clear_close_on_exec(fd, fdt); <6>[ 442.695354] [<ffffffc00021d084>] warn_slowpath_fmt+0x4c/0x58 <6>[ 442.695359] [<ffffffc0002461a8>] __clear_bit+0x98/0xa4 <6>[ 442.695367] [<ffffffc000312340>] dup_fd+0x1d4/0x280 <6>[ 442.695375] [<ffffffc00021b07c>] copy_process.part.56+0x42c/0xe38 <6>[ 442.695382] [<ffffffc00021bb9c>] do_fork+0xe0/0x360 <6>[ 442.695389] [<ffffffc00021beb4>] 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-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
