Re: [PATCH] Display active jiffie timers in /proc/timer_list

On Tue, 25 Nov 2008, Joe Korty wrote:

On Tue, Nov 25, 2008 at 04:36:48PM -0500, Thomas Gleixner wrote:

quoted

quoted

--- 2.6.28-rc6.orig/kernel/timer.c    2008-11-25 11:59:07.000000000 -0500
+++ 2.6.28-rc6/kernel/timer.c 2008-11-25 13:49:05.000000000 -0500
+#if defined(CONFIG_PROC_FS) || defined(CONFIG_MAGIC_SYSRQ)

This belongs into kernel/time/timer_list.c and there is no need to
copy that code around.

Everything to do with jiffy timer implementation is static
local to kernel/timer.c, and not available to code in
kernel/time/timer_list.c or anywhere else.  I consider that
localization to be a rather nice feature of kernel/timer.c,
and I wasn't willing to globalize it just for a debug
data dump.

Also, other features implement their 'show' functions
elsewhere, for example, show_interrupts.  So doing the
same thing here is certainly not out of line.

I prefer a global variable over duplicate code and stuff which I have
to find out from random places.

show_interrupts is arch specific. timers are not.
 

quoted

quoted

+void print_cpu_jtimers(struct seq_file *m, int cpu)
+{
+     int i;
+     struct tvec_base *base = per_cpu(tvec_bases, cpu);
+
+     SEQ_printf(m, "active jiffie timers:\n");
+     spin_lock_irq(&base->lock);

Yuck. We really do _NOT_ stop everything just to print timers. Check
the hrtimer print code in timer_list.c

I'm not sure there is a safe way to reference the timers without
holding the lock.  But I will look into this and see what can
be done.

 
You can't do a real snapshot of the timer wheel. All you can do is
walk it carefully and make a copy of the timer_list structure and then
print it. The timer wheel can be pretty full and we definitely do not
want to stop a CPU fully just to print debug information.

quoted

quoted

              P_ns(idle_expires);
-             SEQ_printf(m, "jiffies: %Lu\n",
+             SEQ_printf(m, "jiffies: %llu (0x%llx)\n",
+                        (unsigned long long)jiffies,
                         (unsigned long long)jiffies);

The exact purpose of this change ?

In the 'active jiffie timer' section I print timer_jiffies
etc in hex format.  It's probably just me, but I found that
to be easier to read than the rather longer decimal format.
So this change was to get a hex version of the global jiffies
out, for easy comparison to values appearing in that section.

Certainly everything can be changed to decimal, if that is
the consensus.

We want a consistent format for all the printouts.
 
Thanks,

	tglx