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

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Date:	Sat, 10 Oct 2009 11:05:20 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 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.  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.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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