linux-kernel - Re: System freezes with high network activity

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Date:	Fri, 16 Mar 2012 18:41:29 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Jose Luis Salas <josacar@...il.com>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Jonathan Nieder <jrnieder@...il.com>
Subject: Re: System freezes with high network activity

On 12/03/2011 02:04 PM, Jose Luis Salas wrote:
> Hi,
>
> attached is the output of the timer_list.
>
> With the nohz option the system is stable too.
>
> Other symptom of the problem is network drops performance to 50% ( 50 Mbps ).
>

Hey Jose,
     Just following up on this old email. Looking at the timer_list.txt 
that you sent, I'm not seeing anything that sticks out as problematic. 
Are you still seeing issues with recent kernels (3.1, 3.2) ?    Is nohz 
still working for you?

I suspect the problem is that the lapic on your machine goes out to 
lunch after longish idle times w/ nohz.  That's why the key-press or 
network traffic wakes the system back up.

Does booting with the following patch (without nohz or any clocksource= 
boot args) fix the issue?

If it does, can you increase the time returned in the patch from 20ms by 
powers of ten until it gets to 2 seconds or you see the problem? If the 
patch below doesn't help, can you drop the value down to 1ms and let me 
know if that affects anything?

thanks
-john

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 95bebaa..8fd2bfa 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -546,6 +546,9 @@ u64 timekeeping_max_deferment(void)
  {
  	unsigned long seq;
  	u64 ret;
+
+	return 20000000ULL; /* 20ms */
+
  	do {
  		seq = read_seqbegin(&timekeeper.lock);


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