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

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Message-ID: <20170424085700.vm2wpn5gac57vb2n@hirez.programming.kicks-ass.net>
Date:   Mon, 24 Apr 2017 10:57:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.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 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?