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

Gregory Haskins
2009-05-08T03:18:18Z

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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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