linux-kernel - Re: [RFC PATCH 0/3] generic hypercall support

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Date:	Thu, 07 May 2009 23:17:49 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Chris Wright <chrisw@...s-sol.org>,
	Gregory Haskins <gregory.haskins@...il.com>,
	Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Anthony Liguori <anthony@...emonkey.ws>
Subject: Re: [RFC PATCH 0/3] generic hypercall support

Marcelo Tosatti wrote:
> On Thu, May 07, 2009 at 08:35:03PM -0300, Marcelo Tosatti wrote:
>   
>> Also for PIO/MMIO you're adding this unoptimized lookup to the 
>> measurement:
>>
>>         pio_dev = vcpu_find_pio_dev(vcpu, port, size, !in);
>>         if (pio_dev) {
>>                 kernel_pio(pio_dev, vcpu, vcpu->arch.pio_data);
>>                 complete_pio(vcpu); 
>>                 return 1;
>>         }
>>
>> Whereas for hypercall measurement you don't. I believe a fair comparison
>> would be have a shared guest/host memory area where you store guest/host
>> TSC values and then do, on guest:
>>
>> 	rdtscll(&shared_area->guest_tsc);
>> 	pio/mmio/hypercall
>> 	... back to host
>> 	rdtscll(&shared_area->host_tsc);
>>
>> And then calculate the difference (minus guests TSC_OFFSET of course)?
>>     
>
> Test Machine: Dell Precision 490 - 4-way SMP (2x2) x86_64 "Woodcrest"
> Core2 Xeon 5130 @2.00Ghz, 4GB RAM.
>
> Also it would be interesting to see the MMIO comparison with EPT/NPT,
> it probably sucks much less than what you're seeing.
>
>   

Agreed.  If you or someone on this thread has such a beast, please fire
up my test and post the numbers.

-Greg


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