Re: 2.6.14-rc4-rt7

[Ingo Molnar]

* Daniel Walker <dwalker@xxxxxxxxxx> wrote:

> I found this latency ~5 minutes after boot up, no load . It looks like 
> vgacon_scroll() has a memset like operation which can grow.

do you have PRINTK_IGNORE_LOGLEVEL enabled? If yes then much of the 
printk code will run with interrupts disabled - hence non-preemptable.  
PRINTK_IGNORE_LOGLEVEL is a debugging feature for developers. I have 
added an extra explanation to the Kconfig, see below.

	Ingo

Index: linux/lib/Kconfig.debug
===================================================================
--- linux.orig/lib/Kconfig.debug
+++ linux/lib/Kconfig.debug
@@ -18,6 +18,11 @@ config PRINTK_IGNORE_LOGLEVEL
 	  distributions disable kernel log messages during
 	  certain phases of system startup.)
 
+	  NOTE: this option also makes printk non-preemptible,
+	  which might improve the output of debugging info or
+	  crash info, but it might also cause latencies if your
+	  kernel is printk-ing alot.
+
 	  Normally you dont need or want this option.
 
 config DEBUG_KERNEL
-
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