[Patch] kenvctrld causes very high cpu load

[Patch] kenvctrld causes very high cpu load

[Joerg Friedrich]

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Hi!

I recently got a Sun Blade 1000.
I encountered the same problem described at
http://ubuntuforums.org/showthread.php?t=297474

The mentioned solution (removing the msleep) and switch to polling mode
is imho no good option.

Problem:
kthread kenvctrld calls wait_for_pin(), attaches itself to the
wait_queue and sets itself INTERRUPTIBLE (unneccesary because
msleep_interruptible does the same). Then it checks if the i2c-query is
already done. Usually this is not the case at first check.

Then kenvctrl calles msleep_interruptible(250). Usually 1 or 2 ms later
the i2c-bus signals by interrupt that the desired operation is done.
The interrupt-handler wakes up all tasks in the wq.
Know kenvctrld is reset to TASK_RUNNING and does about 248 ms sleeping
at kernel priority :-(


the patch attached will switch this to wait_event_interruptible_timeout.
It might be possible to change this line:

	if ((val != -ERESTARTSYS) && (val > 0))  {

to

	if (val > 0)  {

but I was not sure if I can rely on errror codes <0


Please check this patch since I do not know exactly how to proceed.


-- 
Jörg Friedrich

There are only 10 types of people:
Those who understand binary and those who don't.

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--- linux-2.6.20/drivers/sbus/char/bbc_i2c.c.orig	2007-02-15 21:26:56.000000000 +0100
+++ linux-2.6.20/drivers/sbus/char/bbc_i2c.c	2007-02-15 21:28:36.000000000 +0100
@@ -187,19 +187,18 @@
 	bp->waiting = 1;
 	add_wait_queue(&bp->wq, &wait);
 	while (limit-- > 0) {
-		u8 val;
+		long val;
 
-		set_current_state(TASK_INTERRUPTIBLE);
-		*status = val = readb(bp->i2c_control_regs + 0);
-		if ((val & I2C_PCF_PIN) == 0) {
+		val = wait_event_interruptible_timeout(bp->wq,
+			(((*status = readb(bp->i2c_control_regs + 0)) & I2C_PCF_PIN) == 0),
+			msecs_to_jiffies(250));
+		if ((val != -ERESTARTSYS) && (val > 0))  {
 			ret = 0;
 			break;
 		}
-		msleep_interruptible(250);
 	}
 	remove_wait_queue(&bp->wq, &wait);
 	bp->waiting = 0;
-	current->state = TASK_RUNNING;
 
 	return ret;
 }
@@ -340,7 +339,7 @@
 	 */
 	if (bp->waiting &&
 	    !(readb(bp->i2c_control_regs + 0x0) & I2C_PCF_PIN))
-		wake_up(&bp->wq);
+		wake_up_interruptible(&bp->wq);
 
 	return IRQ_HANDLED;
 }

Re: [Patch] kenvctrld causes very high cpu load

[Jurij Smakov]

On Thu, Feb 15, 2007 at 10:08:55PM +0100, Joerg Friedrich wrote:
> Hi!
> 
> I recently got a Sun Blade 1000.
> I encountered the same problem described at
> http://ubuntuforums.org/showthread.php?t)7474

This problem also affects Blade 2000 machines, as mentioned in this 
post on debian-sparc:

http://lists.debian.org/debian-sparc/2007/02/msg00055.html

Joerg's patch seems to be doing the right thing there.

Best regards,
-- 
Jurij Smakov                                           jurij@wooyd.org
Key: http://www.wooyd.org/pgpkey/                      KeyID: C99E03CC