Re: performance trouble

[Peter Lieven <pl@dlh.net>]

On 27.03.2012 13:43, Vadim Rozenfeld wrote:
> On Tuesday, March 27, 2012 12:49:58 PM Peter Lieven wrote:
>> On 27.03.2012 12:40, Vadim Rozenfeld wrote:
>>> On Tuesday, March 27, 2012 11:26:29 AM Peter Lieven wrote:
>>>> On 27.03.2012 11:23, Vadim Rozenfeld wrote:
>>>>> On Tuesday, March 27, 2012 10:56:05 AM Gleb Natapov wrote:
>>>>>> On Mon, Mar 26, 2012 at 10:11:43PM +0200, Vadim Rozenfeld wrote:
>>>>>>> On Monday, March 26, 2012 08:54:50 PM Peter Lieven wrote:
>>>>>>>> On 26.03.2012 20:36, Vadim Rozenfeld wrote:
>>>>>>>>> On Monday, March 26, 2012 07:52:49 PM Gleb Natapov wrote:
>>>>>>>>>> On Mon, Mar 26, 2012 at 07:46:03PM +0200, Vadim Rozenfeld wrote:
>>>>>>>>>>> On Monday, March 26, 2012 07:00:32 PM Peter Lieven wrote:
>>>>>>>>>>>> On 22.03.2012 10:38, Vadim Rozenfeld wrote:
>>>>>>>>>>>>> On Thursday, March 22, 2012 10:52:42 AM Peter Lieven wrote:
>>>>>>>>>>>>>> On 22.03.2012 09:48, Vadim Rozenfeld wrote:
>>>>>>>>>>>>>>> On Thursday, March 22, 2012 09:53:45 AM Gleb Natapov wrote:
>>>>>>>>>>>>>>>> On Wed, Mar 21, 2012 at 06:31:02PM +0100, Peter Lieven wrote:
>>>>>>>>>>>>>>>>> On 21.03.2012 12:10, David Cure wrote:
>>>>>>>>>>>>>>>>>> 		hello,
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Le Tue, Mar 20, 2012 at 02:38:22PM +0200, Gleb Natapov
>>>>> ecrivait :
>>>>>>>>>>>>>>>>>>> Try to add<feature policy='disable' name='hypervisor'/>
>>>>>>>>>>>>>>>>>>> to cpu definition in XML and check command line.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> 	ok I try this but I can't use<cpu model>        to map
> the
>>>>>>>>>>>>>>>>>> 	host cpu
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> (my libvirt is 0.9.8) so I use :
>>>>>>>>>>>>>>>>>>         <cpu match='exact'>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>           <model>Opteron_G3</model>
>>>>>>>>>>>>>>>>>>           <feature policy='disable' name='hypervisor'/>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>         </cpu>
>>>>>>>>>>>>>>>>>> 	
>>>>>>>>>>>>>>>>>> 	(the physical server use Opteron CPU).
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> 	The log is here :
>>>>>>>>>>>>>>>>>> http://www.roullier.net/Report/report-3.2-vhost-net-1vcpu-
>>>>>>>>>>>>>>>>>> cp u.tx t.gz
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> 	And now with only 1 vcpu, the response time is 8.5s,
>>>>>>>>>>>>>>>>>> 	great
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> improvment. We keep this configuration for production : we
>>>>>>>>>>>>>>>>>> check the response time when some other users are
>>>>>>>>>>>>>>>>>> connected.
>>>>>>>>>>>>>>>>> please keep in mind, that setting -hypervisor, disabling
>>>>>>>>>>>>>>>>> hpet and only one vcpu
>>>>>>>>>>>>>>>>> makes windows use tsc as clocksource. you have to make
>>>>>>>>>>>>>>>>> sure, that your vm is not switching between physical
>>>>>>>>>>>>>>>>> sockets on your system and that you have constant_tsc
>>>>>>>>>>>>>>>>> feature to have a stable tsc between the cores in the same
>>>>>>>>>>>>>>>>> socket. its also likely that the vm will crash when live
>>>>>>>>>>>>>>>>> migrated.
>>>>>>>>>>>>>>>> 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!
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> @gleb: do you know whats the state of in-kernel hyper-v
>>>>>>>>>>>>>>>>> timers?
>>>>>>>>>>>>>>>> Vadim is working on it. I'll let him answer.
>>>>>>>>>>>>>>> It would be nice to have synthetic timers supported. But,  at
>>>>>>>>>>>>>>> the moment, I'm only researching  this feature.
>>>>>>>>>>>>>> So it will take months at least?
>>>>>>>>>>>>> I would say weeks.
>>>>>>>>>>>> Is there a way, we could contribute and help you with this?
>>>>>>>>>>> Hi Peter,
>>>>>>>>>>> You are welcome to add  an appropriate handler.
>>>>>>>>>> I think Vadim refers to this HV MSR
>>>>>>>>>> http://msdn.microsoft.com/en-us/library/windows/hardware/ff542633%
>>>>>>>>>> 28 v=vs .85 %29.aspx
>>>>>>>>> This one is pretty simple to support. Please see attachments for
>>>>>>>>> more details. I was thinking about synthetic  timers
>>>>>>>>> http://msdn.microsoft.com/en-
>>>>>>>>> us/library/windows/hardware/ff542758(v=vs.85).aspx
>>>>>>>> is this what microsoft qpc uses as clocksource in hyper-v?
>>>>>>> Yes, it should be enough for Win7 / W2K8R2.
>>>>>> To clarify the thing that microsoft qpc uses is what is implemented by
>>>>>> the patch Vadim attached to his previous email. But I believe that
>>>>>> additional qemu patch is needed for Windows to actually use it.
>>>>> You are right.
>>>>> bits 1 and 9 must be set to on in leaf 0x40000003 and HPET
>>>>> should be completely removed from ACPI.
>>>> could you advise how to do this and/or make a patch?
>>> Gleb mentioned that it properly handled in upstream,
>>> otherwise just comment the entire HPET section in
>>> acpi-dsdt.dsl file.
>> i have upstream bios installed. so -no-hpet should disable hpet completely.
>> can you give a hint, what
>> "bits 1 and 9 must be set to on in leaf 0x40000003" means?
> I mean the following code:
> +        if (hyperv_ref_counter_enabled()) {
> +            c->eax |= HV_X64_MSR_TIME_REF_COUNT_AVAILABLE;
> +            c->eax |= 0x200;
> +        }
>
> Please see attached file for more information.
>
>>>> the stuff you send yesterday is for qemu, right? would
>>>> it be possible to use it in qemu-kvm also?
>>> Yes, but don't forget about kvm patch as well.
>> ok, i will try my best. would you consider your patch a quick hack
>> or do you think it would be worth to be uploaded to the upstream
>> repository?
> It was just a brief attempt from my side, mostly inspirited by our with Gleb
> conversation,  to see what it worth to turn this option on.
> It is not fully tested. It will crash Win8 (as well as the rest of the
> currently introduced hyper-v features).
i can confirm that windows 8 installer does not start and resets the
vm continously. it tries to access hv msr 0x40000021

http://msdn.microsoft.com/en-us/library/windows/hardware/ff542648%28v=vs.85%29.aspx

it is possible to tell the guest that the host is not iTSC (how they 
call it) capable. i will try to hack
a patch for this.

peter

> I wouldn't commit this code without comprehensive testing.
> Vadim.
>> peter
>>
>>>> peter
>>>>
>>>>>> --
>>>>>>
>>>>>> 			Gleb.