Hi Changman, On 07/07/2014 09:45 AM, Changman Lee wrote: > Hello, > > On Fri, Jul 04, 2014 at 11:25:35PM -0700, Jaegeuk Kim wrote: >> To Changman, >> >> Just for sure, can you reproduce this issue in the x86 machine with proper >> benchmarks? (i.e., test_bit_le vs. find_next_bit_le) > > It shows quite a different result of bit_mod_test between server and desktop.
It is possible. And the trend of the result is correct, so I think it is credible. > > CPU i5 x86_64 Ubuntu Server - 3.16.0-rc3 > > [266627.204776] find_next_bit_le test_bit_le > [266627.205319] 1832 1774 > [266627.206223] 1292 1746 > [266627.207092] 1205 1746 > [266627.207876] 914 1746 > [266627.208710] 1082 1746 > [266627.209506] 956 1746 > [266627.210175] 523 1746 > > [266627.211839] 3907 1746 > [266627.212898] 1850 1746 > [266627.214046] 2153 1746 > [266627.215118] 1894 1746 > > > CPU i7 x86_64 Mint Desktop - 3.13.0-24-generic > > [432284.422356] find_next_bit_le test_bit_le > [432284.423470] 3771 3878 > [432284.425400] 2671 3696 > [432284.427221] 2492 3760 > [432284.428908] 1971 3696 > [432284.430640] 2191 3730 > [432284.432323] 1986 3696 > [432284.433741] 1123 3698 > > [432284.437269] 8299 3696 > [432284.439487] 3842 3696 > [432284.441850] 4334 3696 > [432284.444080] 3885 3696 > >> >> To all, >> >> I cautiously suspect that the performances might be different when processing >> f2fs_find_entry, since L1/L2 cache misses due to the intermediate routines >> like >> matching strings can make some effect on it. >> >> But, IMO, it is still worth to investigate this issue and contemplate how to >> detect all ones or not. >> >> Ah, one solution may be using 2 bytes from the reserved space, total 3, to >> indicate how many valid dentries are stored in the dentry block. >> >> Any ideas? > > Agree. In the case of one bits is over than half, test_bit is better > than find_next_bit. So we can decide whether using test_bit or > find_next_bit depending on count of one bits. > > When just comparing test_bit and find_next_bit, I think test_bit is more > effective > in f2fs because let's think about f2fs's dentry management policy. > One dentry bucket is filled then next dentry bucket is filled from > lower to higher level. If empty slots of lower level exist, they are used > first. > So, I guess that one bits are getting more than zero bits as time goes by. Partly agree. IMO, what we seriously care about is *find a suitable slot*, not counting the bitmap, we can gain more benefit from find_next_bit rather than test_bit, not only the efficiency, but also the readability. Thanks, Gu > > Thanks, > >> >> Thanks, >> ------------------------------------------------------------------------------ Open source business process management suite built on Java and Eclipse Turn processes into business applications with Bonita BPM Community Edition Quickly connect people, data, and systems into organized workflows Winner of BOSSIE, CODIE, OW2 and Gartner awards http://p.sf.net/sfu/Bonitasoft _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
