linux-kernel - Re: [RFC PATCH 16/22 -v2] add get_monotonic

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Message-ID: <Pine.LNX.4.58.0801162234340.21116@gandalf.stny.rr.com>
Date:	Wed, 16 Jan 2008 22:39:09 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Paul Mackerras <paulus@...ba.org>
cc:	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	john stultz <johnstul@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Bird <tim.bird@...sony.com>,
	Sam Ravnborg <sam@...nborg.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: [RFC PATCH 16/22 -v2] add get_monotonic_cycles


On Thu, 17 Jan 2008, Paul Mackerras wrote:
>
> It's very hard to do a per-thread counter in the VDSO, since threads
> in the same process see the same memory, by definition.  You'd have to
> have an array of counters and have some way for each thread to know
> which entry to read.  Also you'd have to find space for tens or
> hundreds of thousands of counters, since there can be that many
> threads in a process sometimes.

I was thinking about this. What would also work is just the ability to
read the schedule counter for the current cpu. Now this would require that
the task had a way to know which CPU it was currently on.

-- Steve

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