Re: [PATCH 0/9] Btrfs: improve write ahead log with sub transaction

[Josef Bacik <josef@redhat.com>]

On 05/19/2011 04:11 AM, Liu Bo wrote:
> I've been working to try to improve the write-ahead log's performance,
> and I found that the bottleneck addresses in the checksum items,
> especially when we want to make a random write on a large file, e.g a 4G file.
> 
> Then a idea for this suggested by Chris is to use sub transaction ids and just
> to log the part of inode that had changed since either the last log commit or
> the last transaction commit.  And as we also push the sub transid into the btree
> blocks, we'll get much faster tree walks.  As a result, we abandon the original
> brute force approach, which is "to delete all items of the inode in log",
> to making sure we get the most uptodate copies of everything, and instead
> we manage to "find and merge", i.e. finding extents in the log tree and merging
> in the new extents from the file.
> 
> This patchset puts the above idea into code, and although the code is now more
> complex, it brings us a great deal of performance improvement.
> 
> Beside the improvement of log, patch 8 fixes a small but critical bug of log code
> with sub transaction.
> 
> Here I have some test results to show, I use sysbench to do "random write + fsync".
> 
> ===
> sysbench --test=fileio --num-threads=1 --file-num=2 --file-block-size=4K --file-total-size=8G --file-test-mode=rndwr --file-io-mode=sync --file-extra-flags=  [prepare, run]
> ===
> 
> Sysbench args:
>   - Number of threads: 1
>   - Extra file open flags: 0
>   - 2 files, 4Gb each
>   - Block size 4Kb
>   - Number of random requests for random IO: 10000
>   - Read/Write ratio for combined random IO test: 1.50
>   - Periodic FSYNC enabled, calling fsync() each 100 requests.
>   - Calling fsync() at the end of test, Enabled.
>   - Using synchronous I/O mode
>   - Doing random write test
> 
> Sysbench results:
> ===
>    Operations performed:  0 Read, 10000 Write, 200 Other = 10200 Total
>    Read 0b  Written 39.062Mb  Total transferred 39.062Mb
> ===
> a) without patch:  (*SPEED* : 451.01Kb/sec)
>    112.75 Requests/sec executed
> 
> b) with patch:     (*SPEED* : 4.3621Mb/sec)
>    1116.71 Requests/sec executed
> 

Have you run powerfail tests with this?  I'd like to make sure you
haven't inadvertently messed something up.  Thanks,

Josef