linux-kernel - Re: [RFC][PATCH tip/sched/core] sched/rt: Simplify the IPI rt balancing logic

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Message-ID: <20170424084357.645d6f18@gandalf.local.home>
Date:   Mon, 24 Apr 2017 08:43:57 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Clark Williams <williams@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        John Kacur <jkacur@...hat.com>
Subject: Re: [RFC][PATCH tip/sched/core] sched/rt: Simplify the IPI rt
 balancing logic

On Mon, 24 Apr 2017 10:57:00 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, Apr 21, 2017 at 10:49:29PM -0400, Steven Rostedt wrote:
> > +#ifdef HAVE_RT_PUSH_IPI
> > +	/*
> > +	 * For IPI pull requests, loop across the rto_mask.
> > +	 */
> > +	struct irq_work rto_push_work;
> > +	raw_spinlock_t rto_lock;
> > +	/* These atomics are updated outside of a lock */
> > +	atomic_t rto_loop_next;
> > +	atomic_t rto_loop_start;
> > +	/* These are only updated and read withn rto_lock */
> > +	int rto_loop;
> > +	int rto_cpu;
> > +#endif  
> 
> Don't you think it would make sense to place the rto_lock near the
> variables it protects? And if those atomics are supposed to increase
> performance, do they want to share the same cacheline with the lock?

Good point! I'll update.

-- Steve