linux-kernel - Re: [PATCH 1/2] MN10300: Move asm-arm/cnt32_to

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Date:	Mon, 06 Oct 2008 11:44:22 +0100
From:	David Howells <dhowells@...hat.com>
To:	Nicolas Pitre <nico@....org>
Cc:	dhowells@...hat.com, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	torvalds@...l.org, akpm@...ux-foundation.org,
	linux-am33-list@...hat.com, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] MN10300: Move asm-arm/cnt32_to_63.h to include/linux/

Nicolas Pitre <nico@....org> wrote:

> If so then you're using this interface in an inappropriate way.
> 
> The _absolute_ minimum frequency with which this should be fully 
> executed is once per half period of the base counter.  I hope that in 
> practice it happens far more often than that.

I think you're misunderstanding my contention.

If preemption is enabled, cnt32_to_63() can be called with greater than
minimum frequency and yet reversions can still happen.

The problem is that a process that's half way through executing cnt32_to_63()
can be preempted for a period of time sufficient that when it is rescheduled
and writes __m_cnt_hi, it corrupts it with an out of date value.

David

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