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Date: Wed, 28 Nov 2007 08:58:58 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH 0/2] Open disk images with O_DIRECT
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To: qemu-devel@nongnu.org
Cc: Laurent Vivier <Laurent.Vivier@bull.net>

Samuel Thibault wrote:
> Daniel P. Berrange, le Wed 28 Nov 2007 14:27:39 +0000, a écrit :
>   
>> On Wed, Nov 28, 2007 at 03:02:50PM +0100, Laurent Vivier wrote:
>>     
>>> These patches allow to open file using O_DIRECT and bypass the host I/O cache.
>>>
>>> [PATCH 1/2] Add "directio" parameter to "-drive"
>>>
>>>     Using "directio=on" with "-drive" will open the disk image 
>>>     file using "O_DIRECT".
>>>       
>> I don't see the point in adding a config param for this. If it provides a
>> useful performance improvement (or other benefit) we should enable it by 
>> default all the time.
>>     
>
> That depends on the mileage of the user.  Sometimes it is useful since
> it avoids the duplication of page or buffer cache between the guest and
> the host, sometimes it is not because the guest is not so i/o friendly
> and hence using the host page/buffer cache is useful.
>   

In the very least, I think it should be named something more along the 
lines of "caching=off" or "buffering=off" since that's closer to what 
the hardware concept is without exposing implementation details to the user.

Regards,

Anthony Liguori

> Samuel
>
>
>
>