Re: performance trouble

[Peter Lieven <pl@dlh.net>]

On 22.03.2012 09:33, David Cure wrote:
> Le Thu, Mar 22, 2012 at 09:53:45AM +0200, Gleb Natapov ecrivait :
>> All true. I asked to try -hypervisor only to verify where we loose
>> performance. Since you get good result with it frequent access to PM
>> timer is probably the reason. I do not recommend using -hypervisor for
>> production!
> 	so if I leave cpu as previous (not defined) and only disable
> hpet and use 1 vcpu, it's ok for production ?
this is ok, but windows will use pm timer so you will have bad performance.
> 	Is there a workaround for this PM access ?
there exists old patches from 2010 for in-kernel pmtimer. they work, but 
only
partly. problem here is windows enables the pmtimer overflow interrupt 
which this
patch did not address (amongst other things). i simply ignored it and 
windows ran
nevertheless. but i would not do this in production because i do not 
know which side
effects it might have.

there are to possible solutions:

a) a real in-kernel pmtimer implementation (which does also help other 
systems not only windows)
b) hyper-v support in-kernel at least partly (for the timing stuff). 
this is being worked on by Vadim.

Peter
> 	David.
>