you are correct. man page says "..untill data has been physically
written to the underlying storage".
missed that one.
thank you dave
On Tue, Apr 12, 2011 at 12:52 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> On Tue, Apr 12, 2011 at 10:58:53AM +0300, Raz wrote:
>> Christoph Hello
>> I am testing 2.6.38 with AIM benchmark.
>> I compared 2.6.38 to 2.6.27 and I noticed that 2.6.27 is much better
>> than 2.6.38 hwhen
>> doing sync random writes test over an xfs regular file over native
>> Linux partition on top common sata disk.
>> I git bisected the problem and I reached this SHA1:
>> commit 13e6d5cdde0e785aa943810f08b801cadd0935df
>> Author: Christoph Hellwig <hch@xxxxxx>
>> Date: Mon Aug 31 21:00:31 2009 -0300
>>
>> xfs: merge fsync and O_SYNC handling
>>
>> The guarantees for O_SYNC are exactly the same as the ones we need to
>> make for an fsync call (and given that Linux O_SYNC is O_DSYNC the
>> equivalent is fdadatasync, but we treat both the same in XFS), except
>> with a range data writeout. Jan Kara has started unifying these two
>> path for filesystems using the generic helpers, and I've started to
>> look at XFS.
>> ...
>>
>>
>> The bellow two tests presents the how different performance is before and
>> patch:
>> #test 16) bisect 11
>> ------------------------------------------------------------------------------------------------------------
>> Test Test Elapsed Iteration Iteration Operation
>> Number Name Time (sec) Count Rate (loops/sec) Rate
>> (ops/sec)
>> ------------------------------------------------------------------------------------------------------------
>> 1 sync_disk_rw 30.71 19 0.61869 1583.85
>> Sync Random Disk Writes (K)/second
>> ------------------------------------------------------------------------------------------------------------
>
> That's clearly showing that your sync writes are not hitting the
> disk. IOWs, the sync writes are not synchronous at all. There is
> no way a single SATA drive can do >1500 writes to stable storage
> per second.
>
> IOWs, before this fix, sync writes were broken on your hardware.
>
>> #test 17 ) bisect 12
>> ------------------------------------------------------------------------------------------------------------
>> 1 sync_disk_rw 69.05 1 0.01448 37.07
>> Sync Random Disk Writes (K)/second
>> ------------------------------------------------------------------------------------------------------------
>
> And that's pretty tpyical for a SATA drive where sync writes are
> actually hitting the platter correctly.
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@xxxxxxxxxxxxx
>
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