Date: Sun, 7 May 2006 17:53:56 +0100
From: Russell King <rmk+lkml@arm.linux.org.uk>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Mike Galbraith <efault@gmx.de>, Andi Kleen <ak@suse.de>,
       Christopher Friesen <cfriesen@nortel.com>, linux-kernel@vger.kernel.org
Subject: Re: sched_clock() uses are broken
Message-ID: <20060507165356.GA32453@flint.arm.linux.org.uk>
Mail-Followup-To: Nick Piggin <nickpiggin@yahoo.com.au>,
	Mike Galbraith <efault@gmx.de>, Andi Kleen <ak@suse.de>,
	Christopher Friesen <cfriesen@nortel.com>,
	linux-kernel@vger.kernel.org
References: <44578EB9.8050402@nortel.com> <200605021859.18948.ak@suse.de> <445791D3.9060306@yahoo.com.au> <1146640155.7526.27.camel@homer> <445DE925.9010006@yahoo.com.au> <20060507124307.GA20443@flint.arm.linux.org.uk> <445DEE70.10807@yahoo.com.au> <445DEF6D.1050902@yahoo.com.au> <20060507131825.GC20443@flint.arm.linux.org.uk> <445DF667.309@yahoo.com.au>
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On Sun, May 07, 2006 at 11:30:15PM +1000, Nick Piggin wrote:
> Russell King wrote:
> >On Sun, May 07, 2006 at 11:00:29PM +1000, Nick Piggin wrote:
> >
> >>Nick Piggin wrote:
> >>
> >>
> >>>I stand by my first reply to your comment WRT the API.
> >>
> >>Actually, on rereading, it seems like I was a bit confused about
> >>your proposal. I don't think you specified anyway the units
> >>returned by your new sched_clock(). So it is identical to my
> >>"corrected" interface :\
> >
> >
> >Okay, so that presumably means we have to either stick with what we
> >currently have, or go the whole hog and re-implement the sched_clock()
> >support?
> >
> >IOW, my patch on 2nd May isn't of any use as it currently stands?
> 
> IMO it would probably be best to try to re implement it in one go.
> It shouldn't have spread too far out of kernel/sched.c, and the arch
> code should mostly be implementable in terms of their sched_clock().
> Mundane but not difficult.

Having looked at this several times over the last couple of days, I've
come to the conclusion that I'm not the right person to fix this problem.
I've tried several methods of converting the code, but every time I
remain unconvinced that the changes are provably correct as far as not
missing something, so I end up throwing the changes away and starting
again.

Yes, I admit defeat.

Maybe someone who cares about this stuff[1] (or who sees the problem)
should look into it.

[1] - eg, the original poster on linux-arm-kernel who indirectly pointed
out the sched_clock() issue.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
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