Modifying Samba to skip file system reads for IOZONE READ and REREAD

Andrew Bartlett abartlet at
Sat Oct 29 01:12:09 GMT 2005

On Fri, 2005-10-28 at 19:51 -0500, Iozone wrote:

> Richard,
>         Your post did not include anything about this being a lab
>     experiment, but did offer to provide the hack to disable Iozone
>     accuracy.
>         Perhaps I am a bit overly sensitive, but the post could easily be
>     interpreted, by anyone in the world, as a valid mechanism to
>     blind side Iozone and have their Samba produce outrageous
>     results. There are no comments in the post about the intent
>     of the code.

The key line would be: 'exploring some performance issues'

Indeed, the patch included DEBUG(0) lines to ensure that nobody forgot
it was in there, and could understand the subsequent results.

>     My reading of the post was that this code is available from
>     you for anyone that desired to have it. 

Indeed, as is all our software.  

>  Thus, my reaction
>     to this technique.
>         I've lived in the benchmarking world for many years,
>     seen every dirty trick, and watched the consumers get
>     bit by such optimizations.  When I see something like
>     this, it really gets under my skin.
>         I agree that Iozone should take more care to avoid such
>     activities, and a new version will be available within
>     24 hours to address this issue.

In both IOZONE's role as an independent arbiter of performance, and as a
testing tool, it would seem useful to allow both behaviours, so that we
can again determine how much of our performance problems lie in the
layers above and below Samba.  

This is becoming increasingly important as we move to distributed
file-systems, where significant delays do occur below Samba.

Andrew Bartlett

Andrew Bartlett                      
Samba Developer, SuSE Labs, Novell Inc.
Authentication Developer, Samba Team 
Student Network Administrator, Hawker College
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