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

[liubo <liubo2009@cn.fujitsu.com>]

On 05/23/2011 12:43 PM, Josef Bacik wrote:
> 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,
> 

Yes, I've done this before, and it has nothing serious but a few of
"parent transid verify failed", just the same as Chris had mentioned in the thread.

thanks,
liubo

> Josef
>