Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.32-2

[Eran Mann]

Ingo Molnar wrote:
...

> i've implemented the 'tracing follows the task' logic in the -32-2
> patch, available from the usual place:
>
>     http://redhat.com/~mingo/realtime-preempt/
>
> i've also added a CPU# field and i've reworked latency_trace format, to
> make it more readable. Whenever preempt_wakeup_timing is enabled,
> user-tracing will follow the traced task, if it's disabled then tracing
> will stay on the CPU. No other changes.
...
> 	Ingo

On my machine, disabling CONFIG_LATENCY_TRACE causes the kernel to stop 
reporting preempt latencies. After
# echo 1 > /proc/sys/kernel/preempt_max_latency

/proc/sys/kernel/preempt_max_latency always shows 1 no matter what load 
is on the machine. I´ve seen this behavior since the first time I tried 
to disable CONFIG_LATENCY_TRACE, around V0.7.31.something.

Below is the exact diff between the 2 configs (the one that shows 
latencies and the one that doesn´t). Note that the only intentional 
change is turning off CONFIG_LATENCY_TRACE.
=======================================================
--- /tmp/config-2.6.10-rc2-mm3-V0.7.32-2.lat    2004-12-07 
16:25:03.000000000 +0200
+++ /tmp/config-2.6.10-rc2-mm3-V0.7.32-2.no_lat 2004-12-07 
11:06:19.000000000 +0200
@@ -1,7 +1,7 @@
 #
 # Automatically generated make config: don't edit
 # Linux kernel version: 2.6.10-rc2-mm3-V0.7.32-2
-# Tue Dec  7 11:07:07 2004
+# Mon Dec  6 20:24:09 2004
 #
 CONFIG_X86=y
 CONFIG_MMU=y
@@ -137,6 +137,7 @@
 CONFIG_MTRR=y
 # CONFIG_EFI is not set
 CONFIG_HAVE_DEC_LOCK=y
+# CONFIG_REGPARM is not set

 #
 # Performance-monitoring counters support
@@ -1711,12 +1712,12 @@
 CONFIG_CRITICAL_IRQSOFF_TIMING=y
 CONFIG_CRITICAL_TIMING=y
 CONFIG_LATENCY_TIMING=y
-CONFIG_LATENCY_TRACE=y
-CONFIG_MCOUNT=y
+# CONFIG_LATENCY_TRACE is not set
 # CONFIG_RT_DEADLOCK_DETECT is not set
 # CONFIG_DEBUG_KOBJECT is not set
 CONFIG_DEBUG_BUGVERBOSE=y
 # CONFIG_DEBUG_INFO is not set
+CONFIG_USE_FRAME_POINTER=y
 CONFIG_FRAME_POINTER=y
 CONFIG_EARLY_PRINTK=y
 # CONFIG_DEBUG_STACKOVERFLOW is not set
=======================================================
--
Eran Mann

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