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

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Laurent Vivier wrote:
>>> Le vendredi 07 novembre 2008 à 07:59 -0600, Anthony Liguori a écrit :
>>>   In all cases #1 is totally useless as it is only cosmetic.
>>>
>>> #2 improves performance without aligned buffers and with "cache" set to
>>> default value.
>>>   
>>
>> I'm currently rewriting the block-raw-posix.c O_DIRECT support.  I'll 
>> commit your patches once I finish that.
>>
>> I'm switching everything to use the aio functions, introducing a 
>> memory pool so that we can efficiently allocate memory for new 
>> requests without having unbounded memory allocation, and switching 
>> all the synchronous functions to use the aio functions.
>
> What about locking?  If clusters are already allocated and we don't 
> need COW things are simple (and a global lock should suffice, provided 
> it's released before the io is actually submitted), but are you 
> planning to parallelize the metadata paths as well?

I'm still doing a global lock model and requests submitted while a 
request is pending is simply queued.  There are certainly more effective 
strategies but this will work for now.

My larger goal is to totally eliminate synchronous reads/writes APIs in 
QEMU.  They cause unending pain with the main loop.

Regards,

Anthony Liguori