Re: [PATCH v2 4/4] nmi_backtrace: generate one-line reports for idle cpus

From: Chris Metcalf
Date: Mon Mar 21 2016 - 12:15:36 EST

On 03/21/2016 11:42 AM, Peter Zijlstra wrote:
On Wed, Mar 16, 2016 at 01:02:13PM -0400, Chris Metcalf wrote:
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9f7c21c22477..d569ae7fde37 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -298,7 +298,7 @@ void arch_cpu_idle(void)
* We use this if we don't have any better idle routine..
-void default_idle(void)
+void __cpuidle default_idle(void)
trace_cpu_idle_rcuidle(1, smp_processor_id());
@@ -413,7 +413,7 @@ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
* with interrupts enabled and no flags, which is backwards compatible with the
* original MWAIT implementation.
-static void mwait_idle(void)
+static __cpuidle void mwait_idle(void)
if (!current_set_polling_and_test()) {
trace_cpu_idle_rcuidle(1, smp_processor_id());
The most common idle function for x86 is: mwait_idle_with_hints(),
trouble is, its an inline, so I'm not sure adding __cpuidle to it does

No, you're right, it wouldn't help. I didn't look at the drivers/cpuidle
subsystem at all in my patch, since I'm not that familiar with it,
but it seems like tagging acpi_processor_ffh_cstate_enter(), as the
only user of mwait_idle_with_hints(), will do the job.

I do see that native_play_dead() also uses mwait/monitor, but since
that's hotplug I don't think it's relevant to this patch series.

I've yet to find the magic objdump incantation to check. Or rather
objdump -h doesn't appear to list .cpuidle.text at all :/

I'm probably doing something silly...

The easiest way to check for a given function is just to look
at the "nm -n" output and see that all the functions you expect
to reflect idle behavior are in the cpuidle begin/end range.
Or, to look at "objdump -dr" and search for monitor/mwait.

objdump -h certainly works to show .cpuidle.text if you look at
individual objects (e.g. arch/x86/kernel/process.o) but by the time
you're looking at the linked vmlinux image they have all been linked
into the giant .text section.

Chris Metcalf, Mellanox Technologies