Re: [Qemu-devel] Re: KVM call minutes for Sept 14

[Kevin Wolf]

Am 15.09.2010 15:52, schrieb Anthony Liguori:
> On 09/15/2010 08:30 AM, Kevin Wolf wrote:
>> Am 15.09.2010 15:21, schrieb Anthony Liguori:
>>    
>>> On 09/15/2010 07:38 AM, Kevin Wolf wrote:
>>>      
>>>> No, we don't really care if the L2 entry is on disk. If the guest want
>>>> to have its data safe it needs to issue an explicit flush anyway. The
>>>> only thing we want to achieve with bdrv_write_sync is to maintain the
>>>> right order between metadata updates to survive a crash without corruption.
>>>>
>>>>        
>>> Ah, yes, this is brand new :-)
>>>
>>> I was looking at my QED branch which is a few weeks old.
>>>      
>> Well, the whole bdrv_pwrite_sync thing is new - with your benchmarking
>> you probably caught qcow2 at its worst performance in years.
> 
> FWIW, we queued a run reverting the sync() stuff entirely as we were 
> aware of that.  Should have results this morning.

Okay. I think that will be helpful, even outside the context of QED. I'd
be interested how much of a difference it really makes in your tests.

Kevin