On Wed, 29 Feb 2012, Jacek Luczak wrote: > 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 Hi, I have created a simple script which creates a bunch of files with random names in the directory and then performs operation like list, tar, find, copy and remove. I have run it for ext4, xfs and btrfs with the 4k size files. And the result is that ext4 pretty much dominates the create times, tar times and find times. However copy times is a whole different story unfortunately - is sucks badly. Once we cross the mark of 320000 files in the directory (on my system) the ext4 is becoming significantly worse in copy times. And that is where the hash tree order in the directory entry really hit in. Here is a simple graph: http://people.redhat.com/lczerner/files/copy_benchmark.pdf Here is a data where you can play with it: https://www.google.com/fusiontables/DataSource?snapid=S425803zyTE and here is the txt file for convenience: http://people.redhat.com/lczerner/files/copy_data.txt I have also run the correlation.py from Phillip Susi on directory with 100000 4k files and indeed the name to block correlation in ext4 is pretty much random :) _ext4_ Name to inode correlation: 0.50002499975 Name to block correlation: 0.50002499975 Inode to block correlation: 0.9999900001 _xfs_ Name to inode correlation: 0.969660303397 Name to block correlation: 0.969660303397 Inode to block correlation: 1.0 So there definitely is a huge space for improvements in ext4. Thanks! -Lukas Here is a script I have used to get the numbers above, just to see that are the operation I have performed. #!/bin/bash dev=$1 mnt=$2 fs=$3 count=$4 size=$5 if [ -z $dev ]; then echo "Device was not specified!" exit 1 fi if [ -z $mnt ]; then echo "Mount point was not specified!" exit 1 fi if [ -z $fs ]; then echo "File system was not specified!" exit 1 fi if [ -z $count ]; then count=10000 fi if [ -z $size ]; then size=0 fi export TIMEFORMAT="%3R" umount $dev &> /dev/null umount $mnt &> /dev/null case $fs in "xfs") mkfs.xfs -f $dev &> /dev/null; mount $dev $mnt;; "ext3") mkfs.ext3 -F -E lazy_itable_init $dev &> /dev/null; mount $dev $mnt;; "ext4") mkfs.ext4 -F -E lazy_itable_init $dev &> /dev/null; mount -o noinit_itable $dev $mnt;; "btrfs") mkfs.btrfs $dev &> /dev/null; mount $dev $mnt;; *) echo "Unsupported file system"; exit 1;; esac testdir=${mnt}/$$ mkdir $testdir _remount() { sync #umount $mnt #mount $dev $mnt echo 3 > /proc/sys/vm/drop_caches } #echo "[+] Creating $count files" _remount create=$((time ./dirtest $testdir $count $size) 2>&1) #echo "[+] Listing files" _remount list=$((time ls $testdir > /dev/null) 2>&1) #echo "[+] tar the files" _remount tar=$((time $(tar -cf - $testdir &> /dev/null)) 2>&1) #echo "[+] find the files" _remount find=$((time $(find $testdir -type f &> /dev/null)) 2>&1) #echo "[+] Copying files" _remount copy=$((time $(cp -a ${testdir} ${mnt}/copy)) 2>&1) #echo "[+] Removing files" _remount remove=$((time $(rm -rf $testdir)) 2>&1) echo "$fs $count $create $list $tar $find $copy $remove" -- 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
