Re: [Qemu-devel] [PATCH 0/4] qcow2: Improve cluster refcount update

[Laurent Vivier]

Le jeudi 06 novembre 2008 à 12:53 -0600, Anthony Liguori a écrit :
> Laurent Vivier wrote:
> > This series of patches improves qcow2 performance with O_DIRECT
> > when the qcow2 file is empty and we begin to fill it.
> >   
> 
> I really dislike this series and any future series that does similar 
> things.  The real problem is that non-aligned accesses are so slow, but 
> there's no reason that they must be so slow.  It's because we're doing 
> synchronous IO operations instead of using posix-aio like we should.  
> That's the real problem.  Just doing a memory copy to an aligned buffer 
> is not going to cause that much performance delay.
> 
> We shouldn't be adding more cruft to the code base to avoid fixing the 
> real problem.  I think the current implementation of O_DIRECT needs to 
> be rewritten.

Like any good maintainer, you are becoming a tyrant...

BTW, patch #1 is a clean-up (no change, only code move) and patch #2
doesn't align buffer, but try to minimise syscall (it improves
performance with O_DSYNC too).

Ignore patch #3 and #4 if you dislike them.

Regards,
Laurent
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