linux-kernel - Re: S3 resume regression [1cf4f629d9d2 ("cpu/hotplug: Move online calls to hotplugged cpu")]

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Date:   Mon, 7 Nov 2016 13:49:37 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Feng Tang <feng.79.tang@...il.com>, feng.tang@...el.com,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-arch@...r.kernel.org, Rik van Riel <riel@...hat.com>,
        "Srivatsa S. Bhat" <srivatsa@....edu>,
        Peter Zijlstra <peterz@...radead.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Paul Turner <pjt@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        Len Brown <len.brown@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: S3 resume regression [1cf4f629d9d2 ("cpu/hotplug: Move online
 calls to hotplugged cpu")]

On Tue, Nov 01, 2016 at 10:47:37PM +0200, Ville Syrjälä wrote:
> On Fri, Oct 28, 2016 at 08:58:41PM +0200, Thomas Gleixner wrote:
> > On Fri, 28 Oct 2016, Ville Syrjälä wrote:
> > > On Thu, Oct 27, 2016 at 10:41:18PM +0200, Thomas Gleixner wrote:
> > > > On Thu, 27 Oct 2016, Ville Syrjälä wrote:
> > > > > On Thu, Oct 27, 2016 at 09:25:05PM +0200, Thomas Gleixner wrote:
> > > > > > So it would be interesting whether that hunk in resume_broadcast() is
> > > > > > sufficient.
> > > > > 
> > > > > So far it looks like the answer is yes.
> > > > > 
> > > > > Looks to be about 5 seconds slower than acpi-idle in resuming, but
> > > > > I suppose that's not all that surprising ;)
> > > > 
> > > > Well, set it to 1msec then. If that works reliably then we really can do
> > > > that unconditionally. There is no harm in firing a useless timer during
> > > > resume once.
> > > 
> > > I narrowed down the required timeout, and looks like 25ms is the
> > > minimum that works. With 24ms I already started to have failures. So
> > > maybe just bump it up by an order of magnitude to 250ms for some
> > > safety margin?
> 
> I left the thing running for the weekend and it failed 26 out of 16057
> times with the 25ms timeout. Looks like it takes ~5 minutes to resume
> when it fails, but eventually it does come back.
> 
> > 
> > Sure, but what puzzles me is that we need a timeout that big. What happens
> > between broadcast_resume() and broadcast_resume() + 25ms?
> > 
> > IOW, what is the event/resume function which we need to bridge. We should
> > really try to track than down.
> 
> My hunch would be that SMM trap in the DSDT/SSDT since that's where
> things ended up last time I was tracing these resume problems. Though I
> can't recall if that was just with acpi-idle or if intel_idle landed in
> the same spot as well.
> 
> I guess I can try to repeat that test tomorrow, or I'll try your function
> tracer method if the other thing fails.

I didn't manage to find a lot of time to play around with this, but it
definitely looks like the SMM trap is the problem here. I repeated my
pm_trace experiemnts and when it gets stuck it is trying to execute the
_WAK ACPI method which is where the SMM trap happens.

Maybe the SMM code was written with the expectation of a periodic tick
or something like that?

> 
> > 
> > You might try to enable function tracing and do a tracing_off() when that
> > 25ms timeout fires.
> > 
> > Something like 
> > 
> > 	stop_trace = true;
> > 
> > in broadcast_resume() and then in the broadcast timer function:
> > 
> > 	if (stop_trace) {
> > 		stop_trace = false;
> > 		tracing_off();
> > 	}
> > 
> > Then when the machine is up read the trace, compress and upload it
> > somewhere or send it in private mail if it's not that big.
> > 
> > Thanks,
> > 
> > 	tglx
> 
> 
> -- 
> Ville Syrjälä
> Intel OTC

-- 
Ville Syrjälä
Intel OTC