Re: [PATCH] suppress needless timer reprogramming {tick-sched.c} - test/comment

[Koen Kooi]

Op 5 aug 2008, om 14:14 heeft Tony Lindgren het volgende geschreven:

* Koen Kooi <[EMAIL PROTECTED]> [080805 15:11]:

Op 19 jun 2008, om 14:54 heeft Woodruff, Richard het volgende
geschreven:

Hi,


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

things like MUSB.

I'll resend this to the omap list. I had originally sent it with some dynamic tick enabled it can double performance of high rate interrupt

chance it can to into git?

This patch has been working for me quite well these last few week, any

This needs to go in via LKML, I think Thomas Gleixner is looking into it.

regards,

Koen

Great! It seems that the bulk of the patches OE applies to the beagleboard kernel are on their way into upstream :)

Tony

regards,

Koen

If anyone wants I'll re-send larger trace pictures individually.

From: Woodruff, Richard, Monday, June 16, 2008 7:06 PM


already is the last event programmed in the hardware.  If it is it
skips
calling the hardware.


very short period of time.  The system spends a lot of time
reprogramming the hardware timer which is in a slower timing domain
as

of
time waiting for the timer posting to be done.  All of this
reprogramming is useless as the wake up time has not changed.


almost 60% CPU load down to 15% during high interrupt rate.  If you
like
I can send traces to show this.

It simply does a check to see if the about to be reprogrammed 1 shot In my device I get many interrupts from a high speed USB device in a compared to the CPU. This results in the CPU spending a huge amount As measured using ETM trace this drops my reprogramming penalty from

Attached are some results on OMAP-ARM from USB-OTG:

As host:

[EMAIL PROTECTED] /]# mount -t vfat /dev/sda1 /mnt/
[EMAIL PROTECTED] /]# time -p cp /mnt/OE.mtn.bz2 /dev/null
real 32.51
user 0.02
sys 1.05
[EMAIL PROTECTED] /]# umount /mnt/
[EMAIL PROTECTED] /]# mount -t vfat /dev/sda1 /mnt/
[EMAIL PROTECTED] /]# 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.

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
+               */

+                                  delta_jiffies);
+
+               /* Skip reprogram of event if its not changed */
+               if(ts->tick_stopped && ktime_equal(expires, dev-

Pictures clearly show before a domination by timer reprogram and after + expires = ktime_add_ns(last_update, tick_period.tv64 *

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;
              }

-               /*

-                * timer
-                */

-                                      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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