linux-kernel - Re: [RFC patch 08/18] cnt32_to_63 should use smp

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Message-ID: <8481.1226077497@redhat.com>
Date:	Fri, 07 Nov 2008 17:04:57 +0000
From:	David Howells <dhowells@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	dhowells@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
	Nicolas Pitre <nico@....org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
	benh@...nel.crashing.org, paulus@...ba.org,
	David Miller <davem@...emloft.net>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-arch@...r.kernel.org
Subject: Re: [RFC patch 08/18] cnt32_to_63 should use smp_rmb()

Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:

> First off, using this macro with get_cycles() is simply buggy, because the
> macro expects _perfect_ order of timestamps, no skew whatsoever, or
> otherwise time could jump.

Erm...  Why can't I pass it get_cycles()?  Are you saying that sched_clock()
in MN10300 is wrong for it's use of get_cycles() with cnt32_to_63()?

> 	__x.lo = readl(cnt_lo); /* mmio read */

readl() might insert an extra barrier instruction.  Not only that, io_addr
must be unsigned long.

David
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