Re: compilebench numbers for ext4

[Mingming Cao <cmm@us.ibm.com>]

On Mon, 2007-10-22 at 19:31 -0400, Chris Mason wrote:
> Hello everyone,
> 
> I recently posted some performance numbers for Btrfs with different
> blocksizes, and to help establish a baseline I did comparisons with
> Ext3.
> 

Thanks for doing this, Chris!

> The graphs, numbers and a basic description of compilebench are here:
> 
> http://oss.oracle.com/~mason/blocksizes/
> 
> Ext3 easily wins the read phase, but scores poorly while creating files
> and deleting them.  Since ext3 is winning the read phase, we can assume
> the file layout is fairly good.  I think most of the problems during the
> write phase are caused by pdflush doing metadata writeback.  The file
> data and metadata are written separately, and so we end up seeking
> between things that are actually close together.
> 
> Andreas asked me to give ext4 a try, so I grabbed the patch queue from
> Friday along with the latest Linus kernel.  The FS was created with:
> 
> mkfs.ext3 -I 256 /dev/xxxx
> mount -o delalloc,mballoc,data=ordered -t ext4dev /dev/xxxx
> 
> I did expect delayed allocation to help the write phases of
> compilebench, especially the parts where it writes out .o files in
> random order (basically writing medium sized files all over the
> directory tree).

Unfortunately delayed allocation support for ordered mode is not there
yet. 

>   But, every phase except reads showed huge
> improvements.
> 
> http://oss.oracle.com/~mason/compilebench/ext4/ext-create-compare.png
> http://oss.oracle.com/~mason/compilebench/ext4/ext-compile-compare.png
> http://oss.oracle.com/~mason/compilebench/ext4/ext-read-compare.png
> http://oss.oracle.com/~mason/compilebench/ext4/ext-rm-compare.png
> 
> To match the ext4 numbers with Btrfs, I'd probably have to turn off data
> checksumming...
> 
> But oddly enough I saw very bad ext4 read throughput even when reading
> a single kernel tree (outside of compilebench).  The time to read the
> tree was almost 2x ext3.  Have others seen similar problems?
> 
thanks for point this out, will run compilebench. 

Trying to understand the Disk IO graph
http://oss.oracle.com/~mason/compilebench/ext4/ext-read-compare.png
it looks like ext3 the blocks are spread over the disk, while ext4 is
more around the same place, is this right?

> I think the ext4 delete times are so much better than ext3 because this
> is a single threaded test.  delayed allocation is able to get
> everything into a few extents, and these all end up in the inode.  So,
> the delete phase only needs to seek around in small directories and
> seek to well grouped inodes.  ext3 probably had to seek all over for
> the direct/indirect blocks.
> 
> So, tomorrow I'll run a few tests with delalloc and mballoc
> independently, but if there are other numbers people are interested in,
> please let me know.
> 
> (test box was a desktop machine with single sata drive, barriers were
> not used).
> 
> -chris
> -
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