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

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Date:	Wed, 16 Jan 2008 18:50:26 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	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>,
	Paul Mackerras <paulus@...ba.org>,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: [RFC PATCH 16/22 -v2] add get_monotonic_cycles


On Wed, 16 Jan 2008, Mathieu Desnoyers wrote:
>
> > -	cycle_t offset = (now - cs->cycle_last) & cs->mask;
> > +	/* First update the monotonic base portion.
> > +	 * The dual array update method allows for lock-free reading.
> > +	 */
> > +	int num = !cs->base_num;
> > +	cycle_t offset = (now - cs->base[!num].cycle_base_last);
>
> !0 is not necessarily 1. This is why I use cpu_synth->index ? 0 : 1 in

How about simply "cpu_synth->index ^ 1"? Seems the best choice if you ask
me, if all you are doing is changing it from 1 to zero and back to 1.

-- Steve

> my code. The two previous lines seems buggy. (I did the same mistake in
> my first implementation) ;)
>
> > +	offset &= cs->mask;
> > +	cs->base[num].cycle_base = cs->base[!num].cycle_base + offset;
>
> Here too.
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