linux-kernel - Re: [kerneloops] regression in 2.6.27 wrt "lock

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Message-ID: <20081014210404.GJ10429@nb.net.home>
Date:	Tue, 14 Oct 2008 23:04:04 +0200
From:	Karel Zak <kzak@...hat.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [kerneloops] regression in 2.6.27 wrt "lock_page" and the
	"hwclock" program

On Mon, Oct 13, 2008 at 10:55:59AM -0400, Arjan van de Ven wrote:
> Karel: Can you describe what it WANTS to do so we can see if we can

 It wants to "atomically" (without context switch) read/write time
 from CMOS. This is unrealistic of course.

> just extend the linux kernel to do that the right way?

 The kernel is already extended and hwclock uses the extension :-)
 The solution is /dev/rtc.

 The code that directly works with CMOS is fallback solution for
 people who don't want or can not use the standard RTC device. I guess
 people use this functionally for experiments only. Today the RTC
 framework should work everywhere.

 I'll simply remove the "cli" / "sti" code -- eventually I can try
 to optimize it by mlockall() and SCHED_FIFO (as suggested by Linus).

    Karel

-- 
 Karel Zak  <kzak@...hat.com>
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