linux-kernel - Re: [patch 01/18] x86, bts: fix race when bts tracer is removed

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Date:	Fri, 3 Apr 2009 13:30:58 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Metzger, Markus T" <markus.t.metzger@...el.com>
Cc:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"markus.t.metzger@...il.com" <markus.t.metzger@...il.com>,
	"roland@...hat.com" <roland@...hat.com>,
	"eranian@...glemail.com" <eranian@...glemail.com>,
	"oleg@...hat.com" <oleg@...hat.com>,
	"Villacis, Juan" <juan.villacis@...el.com>,
	"ak@...ux.jf.intel.com" <ak@...ux.jf.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [patch 01/18] x86, bts: fix race when bts tracer is removed


* Metzger, Markus T <markus.t.metzger@...el.com> wrote:

> >-----Original Message-----
> >From: Metzger, Markus T
> >Sent: Friday, April 03, 2009 8:20 AM
> >To: Ingo Molnar
> 
> 
> >>Also, raw use of jiffies_64 is buggy and racy. Why does this use
> >>jiffies to begin with - why not some finer grained time?
> >
> >What would be a good time to use?
> 
> I found cpu_clock() declared in sched.h, which is based on TSC and 
> seems to be used by the scheduler, as well. Would this be a good 
> time to use?

i'd suggest trace_clock() [which maps to cpu_clock() internally], or 
trace_clock_global().

See kernel/trace/trace_clock.c about the properties/tradeoffs. Since 
this is a user-facing ABI, trace_clock_global() looks more 
compelling, despite its global lock.

	Ingo
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