On 3/17/2016 6:38 PM, Peter Zijlstra wrote:

On Thu, Mar 17, 2016 at 06:31:44PM -0400, Chris Metcalf wrote:

quoted

On 3/17/2016 3:36 PM, Peter Zijlstra wrote:

quoted

On Wed, Mar 16, 2016 at 01:02:10PM -0400, Chris Metcalf wrote:

quoted

Currently you can only request a backtrace of either all cpus, or
all cpus but yourself.  It can also be helpful to request a remote
backtrace of a single cpu, and since we want that, the logical
extension is to support a cpumask as the underlying primitive.

This change modifies the existing lib/nmi_backtrace.c code to take
a cpumask as its basic primitive, and modifies the linux/nmi.h code
to use either the old "all/all_but_self" arch methods, or the new
"cpumask" method, depending on which is available.

The existing clients of nmi_backtrace (arm and x86) are converted
to using the new cpumask approach in this change.

So the past days I've been staring at RCU stall warns, and they can use
a little of this. Their remote stack unwinds are less than useful.

Were you suggesting this as an improvement for a possible v3, or just a
kind of implicit ack of the patch series?  Thanks!

A suggestion more like. I've not actually looked at the 4th patch.

I'll try and fold the patches into the runs I do tomorrow, I'm sure to
trigger lots of fail. Maybe I'll even do that RCU patch.

The build bot caught the fact that I missed arch/xtensa since it doesn't use
LOCK_TEXT, so if you're testing on that (ok maybe unlikely) you can add this:

diff --git a/arch/xtensa/kernel/vmlinux.lds.S b/arch/xtensa/kernel/vmlinux.lds.S
index c417cbe4ec87..18a174c7fb87 100644
--- a/arch/xtensa/kernel/vmlinux.lds.S
+++ b/arch/xtensa/kernel/vmlinux.lds.S

@@ -93,6 +93,9 @@ SECTIONS
      VMLINUX_SYMBOL(__sched_text_start) = .;
      *(.sched.literal .sched.text)
      VMLINUX_SYMBOL(__sched_text_end) = .;
+    VMLINUX_SYMBOL(__cpuidle_text_start) = .;
+    *(.cpuidle.literal .cpuidle.text)
+    VMLINUX_SYMBOL(__cpuidle_text_end) = .;
      VMLINUX_SYMBOL(__lock_text_start) = .;
      *(.spinlock.literal .spinlock.text)
      VMLINUX_SYMBOL(__lock_text_end) = .;

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com