linux-kernel - Re: [PATCH RT] fix IPI balancing for 4.14-rt

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Date:   Mon, 27 Nov 2017 17:25:21 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Clark Williams <williams@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        John Kacur <jkacur@...hat.com>, Scott Wood <swood@...hat.com>,
        Mike Galbraith <efault@....de>
Subject: Re: [PATCH RT] fix IPI balancing for 4.14-rt

On Thu, 23 Nov 2017 18:25:39 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

 
> I cherry-picked commit 4bdced5c9a29 ("sched/rt: Simplify the IPI based
> RT balancing logic") and while refreshing the queue I noticed that the
> irq_work struct moved and added the fix below into the original patch
> where the IRQ_WORK_HARD_IRQ flag was added.

Perhaps you should keep it as a separate patch. 4bdced5c9a29 is now in
mainline. The next time you port to mainline, you may drop this fix,
and cause the scheduling IPI to run in threaded context (which would be
bad).

Having it as a separate patch, would remind us that it would need to be
added to mainline in the future.

Feel free to add to that that patch:

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve


> 
> > -- Steve
> > 
> > Index: linux-rt.git/kernel/sched/topology.c
> > ===================================================================
> > --- linux-rt.git.orig/kernel/sched/topology.c
> > +++ linux-rt.git/kernel/sched/topology.c
> > @@ -257,6 +257,7 @@ static int init_rootdomain(struct root_d
> >  	rd->rto_cpu = -1;
> >  	raw_spin_lock_init(&rd->rto_lock);
> >  	init_irq_work(&rd->rto_push_work, rto_push_irq_work_func);
> > +	rd->rto_push_work.flags |= IRQ_WORK_HARD_IRQ;
> >  #endif
> >  
> >  	init_dl_bw(&rd->dl_bw);  
> 
> Sebastian