linux-kernel - Re: sched_clock

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Message-ID: <4BC8024E.6020006@petalogix.com>
Date:	Fri, 16 Apr 2010 08:23:10 +0200
From:	Michal Simek <michal.simek@...alogix.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	wuzhangjin@...il.com, Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: sched_clock - microblaze

Arnd Bergmann wrote:
> On Thursday 15 April 2010 21:29:27 Michal Simek wrote:
>>> sched_clock() {
>>>       ftrace_stop();
>>>       printk(...);
>>>       ftrace_start();
>>>       ...
>>> }
>> But I am describing different problem. sched_clock is called before 
>> kernel initialized timers. Microblaze takes all information from DTS 
>> that's means that I am not able to read timer because I even don't know 
>> where it is. :-(
> 
> You could make sched_clock return zero before the clock is probed, it
> is very unlikely to be needed before that anyway.

First of all - this technique works.

That calling sequence is
main.c: sched_init() -> sched.c: sched_init(); -> init_idle(); -> 
sched_clock() without initialized timer which is causing my problems.

Why is sched_clock called in init_idle? Do you get any non zero value on 
any ARCH?

Thanks,
Michal

diff --git a/kernel/sched.c b/kernel/sched.c
index 6af210a..bddd918 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5244,7 +5244,7 @@ void __cpuinit init_idle(struct task_struct *idle, 
int cpu)

         __sched_fork(idle);
         idle->state = TASK_RUNNING;
-       idle->se.exec_start = sched_clock();
+       idle->se.exec_start = 0;

         cpumask_copy(&idle->cpus_allowed, cpumask_of(cpu));
         __set_task_cpu(idle, cpu);

-- 
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663
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