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 S1754887AbcG0KiT (ORCPT <rfc822;w@1wt.eu>);
	Wed, 27 Jul 2016 06:38:19 -0400
Received: from mail-wm0-f66.google.com ([74.125.82.66]:33416 "EHLO
	mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752142AbcG0KiS (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 27 Jul 2016 06:38:18 -0400
Date: Wed, 27 Jul 2016 12:38:14 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Rusty Russel <rusty@rustcorp.com.au>
Subject: Re: [PATCH] sched/core: make "Preemption disabled at" message more
 useful
Message-ID: <20160727103814.GB8845@gmail.com>
References: <1469260693-22260-1-git-send-email-vegard.nossum@oracle.com>
 <20160727091527.GB6323@gmail.com>
 <CAOMGZ=EBmgqgwrOmzqJaiGBmyoN7zG5AOEmeQ7LRymY65pHFqw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAOMGZ=EBmgqgwrOmzqJaiGBmyoN7zG5AOEmeQ7LRymY65pHFqw@mail.gmail.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Vegard Nossum <vegard.nossum@gmail.com> wrote:

> On 27 July 2016 at 11:15, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > * Vegard Nossum <vegard.nossum@oracle.com> wrote:
> [...]
> 
> > These two blocks could be merged trivially, avoiding an #ifdef pair ...
> 
> >> @@ -7541,6 +7550,9 @@ EXPORT_SYMBOL(__might_sleep);
> >>  void ___might_sleep(const char *file, int line, int preempt_offset)
> >>  {
> >>       static unsigned long prev_jiffy;        /* ratelimiting */
> >> +#ifdef CONFIG_DEBUG_PREEMPT
> >> +     unsigned long preempt_disable_ip;
> >> +#endif
> >>
> >>       rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
> >>       if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
> >> @@ -7551,6 +7563,11 @@ void ___might_sleep(const char *file, int line, int preempt_offset)
> >>               return;
> >>       prev_jiffy = jiffies;
> >>
> >> +#ifdef CONFIG_DEBUG_PREEMPT
> >> +     /* Save this before calling printk(), since that will clobber it */
> >> +     preempt_disable_ip = current->preempt_disable_ip;
> >> +#endif
> >
> > Ditto.
> 
> I'm assuming you want to declare and initialise preempt_disable_ip at
> once here, but it generates slightly worse code since it dereferences
> current->preempt_disable_ip in the "fast path" (i.e. a sleeping
> function is NOT called from an invalid context).

Could you please add a likely() branch to see whether GCC will delay the 
initialization?

The 4 #ifdefs were really ugly, so yes, it would be nice to at least reduce them 
to 2.

Thanks,

	Ingo