linux-kernel - Re: [PATCH] tracing: fix incorrect return type of ns2usecs()

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Date:	Mon, 30 Mar 2009 11:55:23 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <srostedt@...hat.com>,
	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: fix incorrect return type of ns2usecs()

On Mon, Mar 30, 2009 at 11:52:13AM +0800, Lai Jiangshan wrote:
> 
> Impact: fix time output bug in 32bits system
> 
> ns2usecs() returns 'long', it's incorrect.
> 
> (In i386)
> # cat trace
> ...
>           <idle>-0     [000]   521.442100: _spin_lock <-tick_do_update_jiffies64
>           <idle>-0     [000]   521.442101: do_timer <-tick_do_update_jiffies64
>           <idle>-0     [000]   521.442102: update_wall_time <-do_timer
>           <idle>-0     [000]   521.442102: update_xtime_cache <-update_wall_time
> ....
> (It always print the time less than 2200 seconds besides ...)
> Because 'long' is 32bits in i386. ( (1<<31) useconds is about 2200 seconds)
> 
> # cat trace
> ...
>           <idle>-0     [001] 4154502640.134759: rcu_bh_qsctr_inc <-__do_softirq
>           <idle>-0     [001] 4154502640.134760: _local_bh_enable <-__do_softirq
>           <idle>-0     [001] 4154502640.134761: idle_cpu <-irq_exit
> ...
> (very large value)
> Because 'long' is a signed type and is 32bits in i386.
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> Reported-by: Li Zefan <lizf@...fujitsu.com>
> Tested-by: Lai Jiangshan <laijs@...fujitsu.com>


Acked-by: Frederic Weisbecker <fweisbec@...il.com>

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