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.
> 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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