Subject: Re: [PATCH v2 1/4] nmi_backtrace: add more trigger_*_cpu_backtrace()
 methods
To: Peter Zijlstra <peterz@infradead.org>
References: <1458147733-29338-1-git-send-email-cmetcalf@mellanox.com>
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 <20160317193600.GY6344@twins.programming.kicks-ass.net>
CC: Russell King <linux@arm.linux.org.uk>,
        Thomas Gleixner <tglx@linutronix.de>,
        Aaron Tomlin <atomlin@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@osdl.org>,
        Daniel Thompson <daniel.thompson@linaro.org>, <x86@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>
From: Chris Metcalf <cmetcalf@mellanox.com>
Message-ID: <56EB3050.3060607@mellanox.com>
Date: Thu, 17 Mar 2016 18:31:44 -0400
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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
http://www.mellanox.com