Re: timing in driver function

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Hi,

On Mon, 1 Aug 2011, Michael Jones wrote:

> I have a function in a driver which takes ~50ms to execute, which I've
> measured by reading jiffies at the beginning and end. But jiffies only
> counts at 128Hz on my system, so this was a very coarse measurement. Now
> I would like to find out more exactly where the time is going inside
> this function. So my basic question is, what is the best way to measure
> lapsed time with reasonable resolution on an OMAP?
> 
> As I had done with the jiffies measurement, what I imagined was
> inserting lines into my function, sampling the value of some counter at
> various points within it. This approach is crude but simple and would
> suffice for my case.
> 
> Since it must be a very common task, I thought I'd ask here what the
> recommended approach is. I see a few directions...
> 
> 1. Using the OMAP's 32kHz timer, which is provided as a "struct
> clocksource". It seems like what I would want is to call
> clocksource_32k.read(), but I don't know how to retrieve clocksource_32k.

Consider getnstimeofday().  It's not OMAP-specific; there are several 
examples in the Linux codebase[1]; and if you use a higher-resolution 
clocksource, the resolution should also increase (try disabling 
CONFIG_OMAP_32K_TIMER).


1. http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git&a=search&h=HEAD&st=grep&s=getnstimeofday


- Paul
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