From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932507AbbFEJsh (ORCPT <rfc822;w@1wt.eu>);
	Fri, 5 Jun 2015 05:48:37 -0400
Received: from www.linutronix.de ([62.245.132.108]:34759 "EHLO
	Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S932464AbbFEJsd (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 5 Jun 2015 05:48:33 -0400
Date: Fri, 5 Jun 2015 11:48:20 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
cc: umgwanakikbuti@gmail.com, mingo@elte.hu, ktkhai@parallels.com,
        rostedt@goodmis.org, juri.lelli@gmail.com, pang.xunlei@linaro.org,
        oleg@redhat.com, wanpeng.li@linux.intel.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the
 timer
In-Reply-To: <20150605085205.723058588@infradead.org>
Message-ID: <alpine.DEB.2.11.1506051140120.4155@nanos>
References: <20150605084836.364306429@infradead.org> <20150605085205.723058588@infradead.org>
User-Agent: Alpine 2.11 (DEB 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, 5 Jun 2015, Peter Zijlstra wrote:
>  /*
> + * We require the migration_base for lock_hrtimer_base()/switch_hrtimer_base()
> + * such that hrtimer_callback_running() can unconditionally dereference
> + * timer->base->cpu_base
> + */
> +static struct hrtimer_cpu_base migration_cpu_base = {
> +	.seq = SEQCNT_ZERO(migration_cpu_base),
> +};
> +
> +static struct hrtimer_clock_base migration_base = {
> +	.cpu_base = &migration_cpu_base,
> +};

You can spare that extra migration clock base, because
migration_cpu_base already has clock bases inside.

static struct hrtimer_cpu_base migration_cpu_base = {
	.seq = SEQCNT_ZERO(migration_cpu_base),
};

and do:

    migration_cpu_base.clock_base[CLOCK_MONOTONIC].cpu_base = &migration_cpu_base;

in hrtimer_init.

So migration base becomes: 

#define migration_base	   &migration_cpu_base.clock_base[CLOCK_MONOTONIC]

That's also more efficient in terms of cache because is two adjacent
cache lines instead of two distant ones.

Other than that, this looks good.

Thanks,

	tglx