Re: KVM performance vs. Xen

[Anthony Liguori <anthony@codemonkey.ws>]

Andrew Theurer wrote:
> Avi Kivity wrote:
>> Anthony Liguori wrote:
>>> Avi Kivity wrote:
>>>>>
>>>>> 1) I'm seeing about 2.3% in scheduler functions [that I recognize].
>>>>> Does that seems a bit excessive?
>>>>
>>>> Yes, it is.  If there is a lot of I/O, this might be due to the 
>>>> thread pool used for I/O.
>>>
>>> This is why I wrote the linux-aio patch.  It only reduced CPU 
>>> consumption by about 2% although I'm not sure if that's absolute or 
>>> relative.  Andrew?
> If  I recall correctly, it was 2.4% and relative.  But with 2.3% in 
> scheduler functions, that's what I expected.
>>
>> Was that before or after the entire path was made copyless?
> If this is referring to the preadv/writev support, no, I have not 
> tested with that.

Previously, the block API only exposed non-vector interfaces and bounced 
vectored operations to a linear buffer.  That's been eliminated now 
though so we need to update the linux-aio patch to implement a vectored 
backend interface.

However, it is an apples to apples comparison in terms of copying since 
the same is true with the thread pool.  My take away was that the thread 
pool overhead isn't the major source of issues.

Regards,

Anthony Liguori