Re: How to measure time accurately.

[Jesper Juhl]

On Mon, 28 Mar 2005, Chris Friesen wrote:

> Date: Mon, 28 Mar 2005 23:07:14 -0600
> From: Chris Friesen <cfriesen@xxxxxxxxxx>
> To: krishna <krishna.c@xxxxxxxxxxxxxxxxxx>
> Cc: Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>
> Subject: Re: How to measure time accurately.
> 
> krishna wrote:
> > Hi All,
> > 
> > Can any one tell me how to measure time accurately for a block of C code in
> > device drivers.
> > For example, If I want to measure the time duration of firmware download.
> 
> Most cpus have some way of getting at a counter or decrementer of various
> frequencies.  Usually it requires low-level hardware knowledge and often it
> needs assembly code.
> 
> 
> On ppc you'd use the mftbu/mftbl instructions, as suggested by Lee on x86
> you'd use the rdtsc instruction.
> 

In some cases you can simply count jiffies - depending on how accurate you 
need to time things I'd say that often something like this is adequate :


unsigned long start, time_spent;

start = jiffies;
/* do stuff */
time_spent = jiffies - start;
printk("stuff took %d jiffies (%d seconds)\n", time_spent, time_spent/HZ);


-- 
Jesper Juhl

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