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, >> -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
