linux-kernel - Re: [PATCH -rt] fix setting of preempt_max_latency and preempt

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Message-ID: <20070327191542.GA15514@rhlx01.hs-esslingen.de>
Date:	Tue, 27 Mar 2007 21:15:42 +0200
From:	Andreas Mohr <andi@...x01.fht-esslingen.de>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -rt] fix setting of preempt_max_latency and preempt_thresh on 64 bit systems

Hi,

On Tue, Mar 27, 2007 at 01:19:07PM -0400, Steven Rostedt wrote:
> Ingo,
> 
> I wasn't able to turn on latency tracing on a x86_64 box. Using logdev
> to see what was happening, I found that echoing 0
> into /proc/sys/kernel/preempt_max_latency would only change the max from
> -1ULL to 0xffffffff00000000. Which would keep the max pretty high still.
> 
> The problem is in sysctl.c where preempt_max_latency can be modified. On
> systems where cycle_t is greater than the size of int (x86_64) we only
> write to the 4 LSB.

Maybe fix up all the other myriads of sysctl entries which use a rather
non-precise generic sizeof(int) as well?
Or doesn't that make sense?
Maybe this is because it's security relevant and you'd better make sure
to know *exactly* the number of integers a buffer's length is supposed to be?

Thanks,

Andreas Mohr
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