Re: Ftrace Timer on OMAP3

[Thomas Klute <thomas2.klute@uni-dortmund.de>]

Am 28.05.2012 10:24, schrieb Ming Lei:
> On Mon, May 28, 2012 at 2:56 PM, Hiremath, Vaibhav <hvaibhav@ti.com> wrote:
>> On Fri, May 25, 2012 at 20:49:07, Thomas Klute wrote:
>>> Hi everyone,
>>>
>>> we're having some trouble getting useful results from Ftrace on OMAP3
>>> (Gumstix Overo). As you can see in the example output below, function
>>> duration can't be displayed with a precision higher than about 30.5 us,
>>> which matches the frequency of the 32 kHz platform timer. For OMAP1,
>>> using OMAP_MPU_TIMER instead of CONFIG_OMAP_32K_TIMER should provide
>>> better results [1], but I couldn't find anything similar for OMAP3. Just
>>> setting CONFIG_OMAP_32K_TIMER=N didn't change the results. Did I miss
>>> anything, or isn't there any more precise timer?
>>>
>>
>> I believe you are using mainline kernel here, if yes, you should be enabling
>> the dmtimer using commandline argument, "clocksource="gp_timer".
> 
> Also you need to pass 'nohlt' to kernel since gp_timer can't be kept
> when cpu is idled in deep state.

I use the linux-omap tree, but adding "clocksource=gp_timer nohlt" to
the kernel command line did the trick anyways. :-)

Thanks to both of you!
Thomas