On Thu, 19 Jun 2008 07:54:19 -0500, "Woodruff, Richard"
<r-woodruff2@xxxxxx> wrote:
> Hi,
>
> I'll resend this to the omap list. I had originally sent it with some
> pictures but I guess they were too big for the lists. Individual should
> have got them.
>
> If anyone has the time this is a good to test with. If you have dynamic
> tick enabled it can double performance of high rate interrupt things like
> MUSB.
>
> If anyone wants I'll re-send larger trace pictures individually.
care to send it to my nokia mail?
felipe 'dot' balbi 'at' nokia 'dot' com
I'll take a shot at this patch after summer holidays.
ps: I'm keeping the rest of the mail below so it' ll be
easier for getting the patch at work :-p
>
>
>> From: Woodruff, Richard, Monday, June 16, 2008 7:06 PM
>>
>> It simply does a check to see if the about to be reprogrammed 1 shot
>> already is the last event programmed in the hardware. If it is it skips
>> calling the hardware.
>>
>> In my device I get many interrupts from a high speed USB device in a
>> very short period of time. The system spends a lot of time
>> reprogramming the hardware timer which is in a slower timing domain as
>> compared to the CPU. This results in the CPU spending a huge amount of
>> time waiting for the timer posting to be done. All of this
>> reprogramming is useless as the wake up time has not changed.
>>
>> As measured using ETM trace this drops my reprogramming penalty from
>> almost 60% CPU load down to 15% during high interrupt rate. If you like
>> I can send traces to show this.
>
> Attached are some results on OMAP-ARM from USB-OTG:
>
> As host:
>
> root@OMAP3EVM /]# mount -t vfat /dev/sda1 /mnt/
> [root@OMAP3EVM /]# time -p cp /mnt/OE.mtn.bz2 /dev/null
> real 32.51
> user 0.02
> sys 1.05
> [root@OMAP3EVM /]# umount /mnt/
> [root@OMAP3EVM /]# mount -t vfat /dev/sda1 /mnt/
> [root@OMAP3EVM /]# time -p cp /mnt/OE.mtn.bz2 /dev/null
> real 17.92
> user 0.05
> sys 1.57
>
> As Client:
>
> Attached are some visuals as of client doing gadget zero tests. Pictures
> clearly show before a domination by timer reprogram and after not.
>
> Regards,
> Richard W.
>
>
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index b854a89..ff6b967 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -254,6 +254,17 @@ void tick_nohz_stop_sched_tick(void)
> /* Schedule the tick, if we are at least one jiffie off */
> if ((long)delta_jiffies >= 1) {
>
> + /*
> + * calculate the expiry time for the next timer wheel
> + * timer
> + */
> + expires = ktime_add_ns(last_update, tick_period.tv64 *
> + delta_jiffies);
> +
> + /* Skip reprogram of event if its not changed */
> + if(ts->tick_stopped && ktime_equal(expires,
> dev->next_event))
> + goto out2;
> +
> if (delta_jiffies > 1)
> cpu_set(cpu, nohz_cpu_mask);
> /*
> @@ -304,12 +315,7 @@ void tick_nohz_stop_sched_tick(void)
> goto out;
> }
>
> - /*
> - * calculate the expiry time for the next timer wheel
> - * timer
> - */
> - expires = ktime_add_ns(last_update, tick_period.tv64 *
> - delta_jiffies);
> + /* Mark expiries */
> ts->idle_expires = expires;
>
> if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
> @@ -328,6 +334,7 @@ void tick_nohz_stop_sched_tick(void)
> tick_do_update_jiffies64(ktime_get());
> cpu_clear(cpu, nohz_cpu_mask);
> }
> +out2:
> raise_softirq_irqoff(TIMER_SOFTIRQ);
> out:
> ts->next_jiffies = next_jiffies;
> --
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--
Best Regards,
Felipe Balbi
http://felipebalbi.com
me@xxxxxxxxxxxxxxx
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