linux-kernel - Re: [PATCH RFC] sched: add notifier for process migration

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Date:	Sat, 10 Oct 2009 11:24:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH RFC] sched: add notifier for process migration

On Sat, 2009-10-10 at 11:05 +0200, Avi Kivity wrote:
> On 10/10/2009 09:14 AM, Peter Zijlstra wrote:
> > Why not do something like:
> >
> >      struct {
> > 	u64 tsc;
> > 	u32 aux;
> >      } tscp = rdtscp();
> >
> >      local_time_info = timeinfo[tscp_cpu(tscp)];
> >
> >      /* yay, consistent tsc and timeinfo !! */
> >    
> 
> First, not all processors support rdtscp.

Is that a real issue? If its not supported by the early hardware virt
chips, tough luck, they sucked anyway :-)

>   Second, timeinfo might change 
> at any time due to cpu frequency changes or the entire cpu being 
> migrated, so we need to loop in any case.

Sure.
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