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Message-ID: <CADDYkjRYrKaBvTQ4Pe6bfemL7r5W=AU468uy0krFAEJD45syow@mail.gmail.com> Date: Wed, 29 Feb 2012 15:07:45 +0100 From: Jacek Luczak <difrost.kernel@...il.com> To: linux-ext4@...r.kernel.org, linux-fsdevel <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, linux-btrfs@...r.kernel.org, chris.mason@...cle.com, lczerner@...hat.com Subject: Re: getdents - ext4 vs btrfs performance 2012/2/29 Jacek Luczak <difrost.kernel@...il.com>: > Hi Chris, > > the last one was borked :) Please check this one. > > -jacek > > 2012/2/29 Jacek Luczak <difrost.kernel@...il.com>: >> Hi All, >> >> /*Sorry for sending incomplete email, hit wrong button :) I guess I >> can't use Gmail */ >> >> Long story short: We've found that operations on a directory structure >> holding many dirs takes ages on ext4. >> >> The Question: Why there's that huge difference in ext4 and btrfs? See >> below test results for real values. >> >> Background: I had to backup a Jenkins directory holding workspace for >> few projects which were co from svn (implies lot of extra .svn dirs). >> The copy takes lot of time (at least more than I've expected) and >> process was mostly in D (disk sleep). I've dig more and done some >> extra test to see if this is not a regression on block/fs site. To >> isolate the issue I've also performed same tests on btrfs. >> >> Test environment configuration: >> 1) HW: HP ProLiant BL460 G6, 48 GB of memory, 2x 6 core Intel X5670 HT >> enabled, Smart Array P410i, RAID 1 on top of 2x 10K RPM SAS HDDs. >> 2) Kernels: All tests were done on following kernels: >> - 2.6.39.4-3 -- the build ID (3) is used here for internal tacking of >> config changes mostly. In -3 we've introduced ,,fix readahead pipeline >> break caused by block plug'' patch. Otherwise it's pure 2.6.39.4. >> - 3.2.7 -- latest kernel at the time of testing (3.2.8 has been >> release recently). >> 3) A subject of tests, directory holding: >> - 54GB of data (measured on ext4) >> - 1978149 files >> - 844008 directories >> 4) Mount options: >> - ext4 -- errors=remount-ro,noatime, >> data=writeback >> - btrfs -- noatime,nodatacow and for later investigation on >> copression effect: noatime,nodatacow,compress=lzo >> >> In all tests I've been measuring time of execution. Following tests >> were performed: >> - find . -type d >> - find . -type f >> - cp -a >> - rm -rf >> >> Ext4 results: >> | Type | 2.6.39.4-3 | 3.2.7 >> | Dir cnt | 17m 40sec | 11m 20sec >> | File cnt | 17m 36sec | 11m 22sec >> | Copy | 1h 28m | 1h 27m >> | Remove| 3m 43sec | 3m 38sec >> >> Btrfs results (without lzo comression): >> | Type | 2.6.39.4-3 | 3.2.7 >> | Dir cnt | 2m 22sec | 2m 21sec >> | File cnt | 2m 26sec | 2m 23sec >> | Copy | 36m 22sec | 39m 35sec >> | Remove| 7m 51sec | 10m 43sec >> >> From above one can see that copy takes close to 1h less on btrfs. I've >> done strace counting times of calls, results are as follows (from >> 3.2.7): >> 1) Ext4 (only to elements): >> % time seconds usecs/call calls errors syscall >> ------ ----------- ----------- --------- --------- ---------------- >> 57.01 13.257850 1 15082163 read >> 23.40 5.440353 3 1687702 getdents >> 6.15 1.430559 0 3672418 lstat >> 3.80 0.883767 0 13106961 write >> 2.32 0.539959 0 4794099 open >> 1.69 0.393589 0 843695 mkdir >> 1.28 0.296700 0 5637802 setxattr >> 0.80 0.186539 0 7325195 stat >> >> 2) Btrfs: >> % time seconds usecs/call calls errors syscall >> ------ ----------- ----------- --------- --------- ---------------- >> 53.38 9.486210 1 15179751 read >> 11.38 2.021662 1 1688328 getdents >> 10.64 1.890234 0 4800317 open >> 6.83 1.213723 0 13201590 write >> 4.85 0.862731 0 5644314 setxattr >> 3.50 0.621194 1 844008 mkdir >> 2.75 0.489059 0 3675992 1 lstat >> 1.71 0.303544 0 5644314 llistxattr >> 1.50 0.265943 0 1978149 utimes >> 1.02 0.180585 0 5644314 844008 getxattr >> >> On btrfs getdents takes much less time which prove the bottleneck in >> copy time on ext4 is this syscall. In 2.6.39.4 it shows even less time >> for getdents: >> % time seconds usecs/call calls errors syscall >> ------ ----------- ----------- --------- --------- ---------------- >> 50.77 10.978816 1 15033132 read >> 14.46 3.125996 1 4733589 open >> 7.15 1.546311 0 5566988 setxattr >> 5.89 1.273845 0 3626505 lstat >> 5.81 1.255858 1 1667050 getdents >> 5.66 1.224403 0 13083022 write >> 3.40 0.735114 1 833371 mkdir >> 1.96 0.424881 0 5566988 llistxattr >> >> >> Why so huge difference in the getdents timings? >> >> -Jacek I will try to answer the question from the broken email I've sent. @Lukas, it was always a fresh FS on top of LVM logical volume. I've been cleaning cache/remounting to sync all data before (re)doing tests. -Jacek BTW: Sorry for the email mixture. I just can't get this gmail thing to work (why forcing top posting:/). 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