linux-kernel - Re: [PATCH RT v2] timer: Raise softirq if there's irq

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Message-ID: <20140125001936.GB9012@linux.vnet.ibm.com>
Date:	Fri, 24 Jan 2014 16:19:36 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <williams@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	John Kacur <jkacur@...hat.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	Joakim Hernberg <jbh@...hemy.lu>,
	Joe Korty <joe.korty@...r.com>,
	Muli Baron <muli.baron@...il.com>
Subject: Re: [PATCH RT v2] timer: Raise softirq if there's irq_work

On Fri, Jan 24, 2014 at 03:35:42PM -0500, Steven Rostedt wrote:
> On Fri, 24 Jan 2014 21:20:39 +0100
> Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:
> 
> > * Steven Rostedt | 2014-01-24 15:09:33 [-0500]:
> > 
> > >[ Talking with Sebastian on IRC, it seems that doing the irq_work_run()
> > >  from the interrupt in -rt is a bad thing. Here we simply raise the
> > >  softirq if there's irq work to do. This too boots on my i7 ]
> > 
> > It is okay in general because most of the users should not run in bare
> > interrupt context. The only exception here is the nohz_full_kick_work
> > thing.
> 
> I know we discussed this on IRC, but I wanted to publicly state that
> the missing irq work callback was the RCU's rsp_wakeup() function.

Failing to invoke rsp_wakeup() when it was needed could potentially
stop RCU grace periods from happening, so having rsp_wakeup() happen
when it is needed is pretty important...

But I would guess that you knew that already.  ;-)

							Thanx, Paul

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