linux-kernel - Re: [tip:sched/core] sched/core: Add debugging code to catch missing update_rq

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Date:   Fri, 03 Feb 2017 13:59:34 +0100
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Sachin Sant <sachinp@...ux.vnet.ibm.com>
Cc:     Ross Zwisler <zwisler@...il.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Michael Ellerman <mpe@...erman.id.au>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [tip:sched/core] sched/core: Add debugging code to catch
 missing update_rq_clock() calls

On Fri, 2017-02-03 at 09:53 +0100, Peter Zijlstra wrote:
> On Fri, Feb 03, 2017 at 10:03:14AM +0530, Sachin Sant wrote:

> > I ran few cycles of cpu hot(un)plug tests. In most cases it works except one
> > where I ran into rcu stall:
> > 
> > [  173.493453] INFO: rcu_sched detected stalls on CPUs/tasks:
> > [  173.493473] > > 	> > 8-...: (2 GPs behind) idle=006/140000000000000/0 softirq=0/0 fqs=2996 
> > [  173.493476] > > 	> > (detected by 0, t=6002 jiffies, g=885, c=884, q=6350)
> 
> Right, I actually saw that too, but I don't think that would be related
> to my patch. I'll see if I can dig into this though, ought to get fixed
> regardless.

FWIW, I'm not seeing stalls/hangs while beating hotplug up in tip. (so
next grew a wart?)

	-Mike