linux-kernel - Re: [Xen-devel] [PATCH RFC v2 4/4] xen/arm: account for stolen ticks

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Message-ID: <1367931401.26321.118.camel@zakaz.uk.xensource.com>
Date:	Tue, 7 May 2013 13:56:41 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"marc.zyngier@....com" <marc.zyngier@....com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"will.deacon@....com" <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [PATCH RFC v2 4/4] xen/arm: account for stolen ticks

> > > @@ -301,6 +320,10 @@ static int __init xen_init_events(void)
> > >  
> > >  	on_each_cpu(xen_percpu_init, NULL, 0);
> > >  
> > > +	pv_time_ops.steal_clock = xen_stolen_accounting;
> > > +	static_key_slow_inc(&paravirt_steal_enabled);
> > > +	static_key_slow_inc(&paravirt_steal_rq_enabled);
> > 
> > We don't seem to do this on x86 -- is that a bug on x86 on Xen?
> 
> On x86 we do all the accounting in do_stolen_accounting, called from our
> own interrupt handler (xen_timer_interrupt).
> I don't think we would gain anything by using the common infrastructure,
> we would actually loose the idle ticks accounting we do there.
> 
> Speaking of which, I don't think that pv_time_ops.steal_clock would
> properly increase CPUTIME_IDLE the way we do in do_stolen_accounting.
> 
> How much of an issue is that?

Doesn't the generic account_idle_time handle this?

Ian.

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