Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace() methods

From: Chris Metcalf
Date: Thu Mar 17 2016 - 18:32:14 EST

On 3/17/2016 3:36 PM, Peter Zijlstra wrote:
On Wed, Mar 16, 2016 at 01:02:10PM -0400, Chris Metcalf wrote:
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!

Chris Metcalf, Mellanox Technologies