Hi Jean,
-----Original Message----- From: Jean Pihet [mailto:jean.pihet@newoldbits.com] Sent: Monday, September 06, 2010 9:53 PM To: Sripathy, Vishwanath Cc: Shilimkar, Santosh; Amit Kucheria; Kevin Hilman; linaro-dev@lists.linaro.org; linux-omap@vger.kernel.org Subject: Re: [PATCH] OMAP CPUIDLE: CPU Idle latency measurement
Hi Vishwa,
On Mon, Sep 6, 2010 at 1:15 PM, Sripathy, Vishwanath vishwanath.bs@ti.com wrote:
I did some profiling of assembly code on OMAP3630 board (ZOOM3). In worst case
it takes around 3.28ms and best case around 2.93ms for mpu off mode. Can you give a bit more details? Which measurement has been taken (ASM only, sleep, wake-up ...?) and what are the significant figures?
Measurement has been done for save (as part of sleep sequence) and restore routine (part of wake up sequence) in assembly code. The above number indicates total time spent in save and restore of ARM context.
For MPU INACTIVE/RET, it is less than 30us.
Mmh that is the resolution of the 32kHz timer, so I guess you get either 0 or 1 timer cycle depending when you start the measurement. IMO the 32kHz timer is too slow to measure those fast events.
Yes I agree. When we use trace events, I believe it would be more accurate as it is based on ARM perf counters.
Vishwa
However as Kevin mentioned in other email, it would be better to find out a way to
trace inside assembly code as well. OK that could be done but first I would like to make sure such a complication is needed.
Regards Vishwa
Jean