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Date: Mon, 5 Mar 2012 12:32:45 +0100 From: Jacek Luczak <difrost.kernel@...il.com> To: Chris Mason <chris.mason@...cle.com>, Jacek Luczak <difrost.kernel@...il.com>, Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org, linux-fsdevel <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, linux-btrfs@...r.kernel.org Subject: Re: getdents - ext4 vs btrfs performance 2012/3/4 Jacek Luczak <difrost.kernel@...il.com>: > 2012/3/3 Jacek Luczak <difrost.kernel@...il.com>: >> 2012/3/2 Chris Mason <chris.mason@...cle.com>: >>> On Fri, Mar 02, 2012 at 03:16:12PM +0100, Jacek Luczak wrote: >>>> 2012/3/2 Chris Mason <chris.mason@...cle.com>: >>>> > On Fri, Mar 02, 2012 at 11:05:56AM +0100, Jacek Luczak wrote: >>>> >> >>>> >> I've took both on tests. The subject is acp and spd_readdir used with >>>> >> tar, all on ext4: >>>> >> 1) acp: http://91.234.146.107/~difrost/seekwatcher/acp_ext4.png >>>> >> 2) spd_readdir: http://91.234.146.107/~difrost/seekwatcher/tar_ext4_readir.png >>>> >> 3) both: http://91.234.146.107/~difrost/seekwatcher/acp_vs_spd_ext4.png >>>> >> >>>> >> The acp looks much better than spd_readdir but directory copy with >>>> >> spd_readdir decreased to 52m 39sec (30 min less). >>>> > >>>> > Do you have stats on how big these files are, and how fragmented they >>>> > are? For acp and spd to give us this, I think something has gone wrong >>>> > at writeback time (creating individual fragmented files). >>>> >>>> How big? Which files? >>> >>> All the files you're reading ;) >>> >>> filefrag will tell you how many extents each file has, any file with >>> more than one extent is interesting. (The ext4 crowd may have better >>> suggestions on measuring fragmentation). >>> >>> Since you mention this is a compile farm, I'm guessing there are a bunch >>> of .o files created by parallel builds. There are a lot of chances for >>> delalloc and the kernel writeback code to do the wrong thing here. >>> >> > [Most of files are B and K size] >> >> All files scanned: 1978149 >> Files fragmented: 313 (0.015%) where 11 have 3+ extents >> Total size of fragmented files: 7GB (~13% of dir size) > > BTRFS: Non of files according to filefrag are fragmented - all fit > into one extent. > >> tar cf on fragmented files: >> 1) time: 7sec >> 2) sw graph: http://91.234.146.107/~difrost/seekwatcher/tar_fragmented.png >> 3) sw graph with spd_readdir: >> http://91.234.146.107/~difrost/seekwatcher/tar_fragmented_spd.png >> 4) both on one: >> http://91.234.146.107/~difrost/seekwatcher/tar_fragmented_pure_spd.png > > BTRFS: tar on ext4 fragmented files > 1) time: 6sec > 2) sw graph: http://91.234.146.107/~difrost/seekwatcher/tar_fragmented_btrfs.png > >> tar cf of fragmented files disturbed with [40,50) K files (in total >> 4373 files). K files before fragmented M files: >> 1) size: 7.2GB >> 2) time: 1m 14sec >> 3) sw graph: http://91.234.146.107/~difrost/seekwatcher/tar_disturbed.png >> 4) sw graph with spd_readdir: >> http://91.234.146.107/~difrost/seekwatcher/tar_disturbed_spd.png >> 5) both on one: >> http://91.234.146.107/~difrost/seekwatcher/tar_disturbed_pure_spd.png > > BTRFS: tar on [40,50) K and ext4 fragmented > 1) time: 56sec > 2) sw graph: http://91.234.146.107/~difrost/seekwatcher/tar_disturbed_btrfs.png > > New test I've included - randomly selected files: > - size 240MB > 1) ext4 (time: 34sec) sw graph: > http://91.234.146.107/~difrost/seekwatcher/tar_random_ext4.png > 2) btrfs (time: 55sec) sw graph: > http://91.234.146.107/~difrost/seekwatcher/tar_random_btrfs.png Yet another test. The original issue is in the directory data handling. In my case a lot of dirs are introduced due to extra .svn. Let's then see how does tar on those dirs looks like. Number of .svn directories: 61605 1) Ext4: - tar time: 10m 53sec - sw tar graph: http://91.234.146.107/~difrost/seekwatcher/svn_dir_ext4.png - sw tar graph with spd_readdir: http://91.234.146.107/~difrost/seekwatcher/svn_dir_spd_ext4.png 2) Btrfs: - tar time: 4m 35sec - sw tar graph: http://91.234.146.107/~difrost/seekwatcher/svn_dir_btrfs.png - sw tar graph with ext4: http://91.234.146.107/~difrost/seekwatcher/svn_dir_btrfs_ext4.png IMO this is not a writeback issue (well it could be but then it mean that it broken in general), it's not fragmentation. Sorting files in readdir helps a bit but is still far behind the btrfs. Any ideas? Is this a issue or the things are like they are and one need to live with it. -Jacek -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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