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

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Message-ID: <20090507234311.GA9517@amt.cnet>
Date:	Thu, 7 May 2009 20:43:11 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Gregory Haskins <ghaskins@...ell.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

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.

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