linux-kernel - Re: [PATCH v2 5/6] KVM-GST: adjust scheduler cpu power

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Date:	Tue, 01 Feb 2011 19:59:31 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Glauber Costa <glommer@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com, Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v2 5/6] KVM-GST: adjust scheduler cpu power

On Tue, 2011-02-01 at 14:22 -0200, Glauber Costa wrote:
> 
> 
> Which tick accounting? In your other e-mail , you pointed that this only
> runs in touch_steal_time, which is fine, will change.

That tick ;-), all the account_foo muck is per tick.

>  But all the rest
> here, that is behind the hypervisor specific vs generic code has nothing
> to do with ticks at all.

But I don't get it, there is no generic code needed, all that's needed
is u64 steal_time_clock(int cpu), and the first part of your
kvm_account_steal_time() function is exactly that if you add the cpu
argument.

+static u64 steal_time_clock(int cpu)
+{
+       u64 steal_time;
+       struct kvm_steal_time *src;
+       int version;
+
+	preempt_disable();
+       src = &per_cpu_ptr(steal_time, cpu);
+       do {
+               version = src->version;
+               rmb();
+               steal_time = src->steal;
+               rmb();
+       } while ((src->version & 1) || (version != src->version));
+       preempt_enable();
+
+       return steal_time
+}

And you're done.. no need to for any of that steal_time_{read,write} business.

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