Benoit,

On Fri, Aug 27, 2010 at 12:25 PM, Cousson, Benoit <b-cous...@ti.com> wrote:
>> This patch has instrumentation code for measuring latencies for
>> various CPUIdle C states for OMAP. Idea here is to capture the
>> timestamp at various phases of CPU Idle and then compute the sw
>> latency for various c states. For OMAP, 32k clock is chosen as
>> reference clock this as is an always on clock. wkup domain memory
>> (scratchpad memory) is used for storing timestamps. One can see the
>> worstcase latencies in below sysfs entries (after enabling
>> CONFIG_CPU_IDLE_PROF
>> in .config). This information can be used to correctly configure cpu idle
>> latencies for various C states after adding HW latencies for each of
>> these sw latencies.
>> /sys/devices/system/cpu/cpu0/cpuidle/state<n>/actual_latency
>> /sys/devices/system/cpu/cpu0/cpuidle/state<n>/sleep_latency
>> /sys/devices/system/cpu/cpu0/cpuidle/state<n>/wkup_latency
>
> FYI, Jean is currently working on using standard Linux probes in order to
> instrument CPUIdle / CPUfreq. I'm not sure it is doable, but it might better
> to use standard method to do that instead of purely OMAP3 specific stuff.
> This code will not scale easily on OMAP4.
The proposed code looks OK to me since it is exporting the cpuidle
latency figures through the generic cpuidle driver (in
drivers/cpuidle/sysfs.c, via
/sys/devices/system/cpu/cpu0/cpuidle/state<n>/).
Once that code gets approved I can (and will) add some trace points in
it, so that all PM related events can be traced vs time.


>
> Do you have a dump of the latency you measured do far?

Jean

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