Ftrace Timer on OMAP3

Ftrace Timer on OMAP3

[Thomas Klute]

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?

Best regards,
Thomas Klute

[1]
http://elinux.org/images/0/0c/Bird-LS-2009-Measuring-function-duration-with-ftrace.pdf

Example Ftrace output:

  876.252136 |   0)               |  sys_sendmsg() {
  876.252166 |   0)               |    rom_rtadd() {
  876.252197 |   0)   0.000 us    |      release_queue_for_dst();
  876.252197 |   0)   0.000 us    |      add_route();
  876.252197 |   0) + 30.517 us   |    }
  876.252258 |   0) + 91.553 us   |  }
--
  876.311859 |   0)               |  sys_sendmsg() {
  876.311889 |   0)               |    rom_rtadd() {
  876.311889 |   0) + 30.518 us   |      release_queue_for_dst();
  876.311920 |   0)   0.000 us    |      add_route();
  876.311920 |   0) + 30.518 us   |    }
  876.311950 |   0) + 91.552 us   |  }
--
  876.371704 |   0)               |  sys_sendmsg() {
  876.371765 |   0)               |    rom_rtadd() {
  876.371765 |   0)   0.000 us    |      release_queue_for_dst();
  876.371765 |   0)   0.000 us    |      add_route();
  876.371795 |   0) + 30.517 us   |    }
  876.371826 |   0) ! 122.071 us  |  }

RE: Ftrace Timer on OMAP3

[Hiremath, Vaibhav]

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".

Thanks,
Vaibhav

Re: Ftrace Timer on OMAP3

[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.

Thanks,
--
Ming Lei

Re: Ftrace Timer on OMAP3

[Thomas Klute]

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