Re: [uml-devel] umls unresponsive & consuming 100% cpu time

[Jeff Dike <jdike@addtoit.com>]

On Wed, May 14, 2008 at 11:41:18AM +0300, Sakari Ailus wrote:
> I have three UML instances running on a host. First, they all were 
> unresponsive simultaneously using all CPU time they could get. After a 
> while they became responsive again. I could log in through SSH. The 
> funny thing is that the date command showed correct date and time (as 
> far as I remember, can't test it now as they are hung again) while the 
> time in bash prompt was constant showing the time around the initial 
> hang, which is the same on all three instances.

I reproduced and debugged a similar problem, resulting in the patch
below.  See if it makes any difference for you...

	       	  	Jeff

-- 
Work email - jdike at linux dot intel dot com

Index: 2.6/stable/arch/um/os-Linux/time.c
===================================================================
--- 2.6.orig/stable/arch/um/os-Linux/time.c	2008-05-14 14:55:56.000000000 -0400
+++ 2.6/stable/arch/um/os-Linux/time.c	2008-05-14 15:30:48.000000000 -0400
@@ -66,12 +66,21 @@ long long disable_timer(void)
 	return timeval_to_ns(&time.it_value);
 }
 
+static long long last_time;
+
 long long os_nsecs(void)
 {
 	struct timeval tv;
+	long long ret;
 
 	gettimeofday(&tv, NULL);
-	return timeval_to_ns(&tv);
+	ret = timeval_to_ns(&tv);
+
+	if((last_time != 0) && (last_time > ret))
+		ret = last_time;
+
+	last_time = ret;
+	return ret;
 }
 
 #ifdef UML_CONFIG_NO_HZ

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