This is a note to let you know that I've just added the patch titled
powerpc: Fix accounting of softirq time when idle
to the 2.6.38-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-fix-accounting-of-softirq-time-when-idle.patch
and it can be found in the queue-2.6.38 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From ad5d1c888e556bc00c4e86f452cad4a3a87d22c1 Mon Sep 17 00:00:00 2001
From: Anton Blanchard <[email protected]>
Date: Sun, 20 Mar 2011 15:28:03 +0000
Subject: powerpc: Fix accounting of softirq time when idle
From: Anton Blanchard <[email protected]>
commit ad5d1c888e556bc00c4e86f452cad4a3a87d22c1 upstream.
commit cf9efce0ce31 (powerpc: Account time using timebase rather
than PURR) used in_irq() to detect if the time was spent in
interrupt processing. This only catches hardirq context so if we
are in softirq context and in the idle loop we end up accounting it
as idle time. If we instead use in_interrupt() we catch both softirq
and hardirq time.
The issue was found when running a network intensive workload. top
showed the following:
0.0%us, 1.1%sy, 0.0%ni, 85.7%id, 0.0%wa, 9.9%hi, 3.3%si, 0.0%st
85.7% idle. But this was wildly different to the perf events data.
To confirm the suspicion I ran something to keep the core busy:
# yes > /dev/null &
8.2%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 10.3%hi, 81.4%si, 0.0%st
We only got 8.2% of the CPU for the userspace task and softirq has
shot up to 81.4%.
With the patch below top shows the correct stats:
0.0%us, 0.0%sy, 0.0%ni, 5.3%id, 0.0%wa, 13.3%hi, 81.3%si, 0.0%st
Signed-off-by: Anton Blanchard <[email protected]>
Signed-off-by: Benjamin Herrenschmidt <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/powerpc/kernel/time.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -356,7 +356,7 @@ void account_system_vtime(struct task_st
}
get_paca()->user_time_scaled += user_scaled;
- if (in_irq() || idle_task(smp_processor_id()) != tsk) {
+ if (in_interrupt() || idle_task(smp_processor_id()) != tsk) {
account_system_time(tsk, 0, delta, sys_scaled);
if (stolen)
account_steal_time(stolen);
Patches currently in stable-queue which might be from [email protected] are
queue-2.6.38/powerpc-fix-accounting-of-softirq-time-when-idle.patch
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