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From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Roland Dreier <rdreier@cisco.com>
Subject: Re: [PATCH -rt] fix setting of preempt_max_latency and preempt_thresh on 64 bit systems
Date: Tue, 27 Mar 2007 21:15:48 +0200	[thread overview]
Message-ID: <20070327191548.GC29929@elte.hu> (raw)
In-Reply-To: <1175015947.19634.6.camel@localhost.localdomain>


* Steven Rostedt <rostedt@goodmis.org> 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.

ah! This should explain Roland Dreier's report about tracing not working 
on x86_64.

> 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.
> 
> Here's the patch:

thanks, applied.

	Ingo

      parent reply	other threads:[~2007-03-27 19:16 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-03-27 17:19 [PATCH -rt] fix setting of preempt_max_latency and preempt_thresh on 64 bit systems Steven Rostedt
2007-03-27 19:15 ` Andreas Mohr
2007-03-27 19:39   ` Steven Rostedt
2007-03-27 19:15 ` Ingo Molnar [this message]

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