linux-kernel - Re: [PATCH 24/32] softirq: Uninline !CONFIG_TRACE_IRQFLAGS __local_bh_disable

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Message-ID: <20190227231438.GF15294@lerouge>
Date:   Thu, 28 Feb 2019 00:14:38 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 24/32] softirq: Uninline !CONFIG_TRACE_IRQFLAGS
 __local_bh_disable_ip()

On Wed, Feb 27, 2019 at 12:14:29PM +0100, Sebastian Andrzej Siewior wrote:
> On 2019-02-12 18:14:15 [+0100], Frederic Weisbecker wrote:
> > diff --git a/include/linux/bottom_half.h b/include/linux/bottom_half.h
> > index 240419382978..ef9e4c752f56 100644
> > --- a/include/linux/bottom_half.h
> > +++ b/include/linux/bottom_half.h
> > @@ -28,17 +28,7 @@ enum
> >  
> >  #define SOFTIRQ_DATA_INIT (SOFTIRQ_ALL_MASK << SOFTIRQ_ENABLED_SHIFT)
> >  
> > -
> > -
> > -#ifdef CONFIG_TRACE_IRQFLAGS
> >  extern void __local_bh_disable_ip(unsigned long ip, unsigned int cnt);
> > -#else
> > -static __always_inline void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
> > -{
> > -	preempt_count_add(cnt);
> > -	barrier();
> > -}
> > -#endif
> 
> you are aware that a simple local_bh_disable() / spin_lock_bh() gains a
> function call. Let me look further how much code you are going to add
> here…

Indeed but as you'll find out, the function is growing beyond reasonable inlining.