Hi,
On Sat, Aug 28, 2010 at 12:08 AM, <vishwanath.sripathy@xxxxxxxxxx> wrote:
> From: Vishwanath BS <vishwanath.sripathy@xxxxxxxxxx>
>
> 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
>
> THis patch is tested on OMAP ZOOM3 using kevin's pm branch.
>
> Signed-off-by: Vishwanath BS <vishwanath.sripathy@xxxxxxxxxx>
> Cc: linaro-dev@xxxxxxxxxxxxxxxx
> ---
...
>
> +#ifdef CONFIG_CPU_IDLE_PROF
> + sleep_time = omap3_sram_get_sleep_time();
> + wkup_time = omap3_sram_get_wkup_time();
> +
> + /* take care of overflow */
> + if (postidle_time < preidle_time)
> + postidle_time += (u32) 0xffffffff;
> + if (wkup_time < sleep_time)
> + wkup_time += (u32) 0xffffffff;
> +
> + idle_time = postidle_time - preidle_time;
> + total_sleep_time = wkup_time - sleep_time;
> + latency = idle_time - total_sleep_time;
> + sleep_time = omap3_sram_get_sleep_time();
> + wkup_time = omap3_sram_get_wkup_time();
Is it needed to re-read the sleep_time and wkup_time values from the scratchpad?
What about the 32k timer overflow? Could that cause the sleep_latency
and/or wkup_latency to be <0?
> +
> + /* calculate average latency after ignoring sprious ones */
> + if ((total_sleep_time > 0) && (latency > state->actual_latency)
> + && (latency >= 0)) {
> + state->actual_latency = CONVERT_32K_USEC(latency);
> + latency = (sleep_time - preidle_time);
Risk of overflow?
> + state->sleep_latency = CONVERT_32K_USEC(latency);
> + latency = postidle_time - wkup_time;
Risk of overflow?
> + state->wkup_latency = CONVERT_32K_USEC(latency);
> + }
> +#endif
> +
> return ts_idle.tv_nsec / NSEC_PER_USEC + ts_idle.tv_sec * USEC_PER_SEC;
> }
>
Jean
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