linux-kernel - Re: [PATCH RT 2/4] Revert "timers: do not raise softirq unconditionally"

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Date:	Thu, 26 Mar 2015 06:23:11 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@...com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	John Kacur <jkacur@...hat.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH RT 2/4] Revert "timers: do not raise softirq
 unconditionally"

On Wed, 2015-03-25 at 20:17 -0600, Thavatchai Makphaibulchoke wrote:
> 
> On 03/22/2015 10:42 PM, Mike Galbraith wrote:
> >> Why can't we just Let swapper be the owner when in irq with no dummy?
> >>
> 
> Thanks Mike for the suggestion.  That may also work. Unfortunately
> somehow I'm still having a hung problem, which may be related to the
> priority of the interrupt handler task.
> 
> >> I have "don't raise timer unconditionally" re-applied, the check for a
> >> running callback bits of my nohz_full fixlet, and the below on top of
> >> that, and all _seems_ well.
> > 
> > But not so well on 64 core box.  That has nothing to do with hacklet
> > though, re-applying timers-do-not-raise-softirq-unconditionally.patch
> > without thta hangs the 64 core box during boot with no help from me
> > other than to patchlet to let nohz work at all, seems there's another
> > issue lurking there.  Hohum.  Without 'don't raise..", big box is fine.
> > 
> 
> If you get your patch to work, I could try my test that was able to
> reproduce the problem consistently.

If you had "don't raise timer unconditionally" applied, no surprise, my
big box hangs too with or without hacklet.  If didn't have it applied,
you don't need the hack.  If you had both and rtmutex debugging turned
on, posted version _should_ explode, as it didn't bother to side-step
that bit (et al).

I plan on taking a poke at getting "don't raise timer unconditionally"
working again when I get myself unburied, and see if I can come up with
a somewhat less icky way to work around take rtmutex in irq naughtiness.

	-Mike

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