linux-kernel - Re: [PATCH 1/2] rt/threadirqs: don't need to save irqs in do

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Message-ID: <20090212232758.GA5865@nowhere>
Date:	Fri, 13 Feb 2009 00:27:58 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] rt/threadirqs: don't need to save irqs in
	do_hardirq()

On Thu, Feb 12, 2009 at 09:24:59PM -0200, Arnaldo Carvalho de Melo wrote:
> Em Thu, Feb 12, 2009 at 07:27:08PM +0100, Frederic Weisbecker escreveu:
> > do_hardirq() has only one caller do_irqd() in a path where irq are already
> > disabled. So we don't need to save irqs while holding desc->lock
> > 
> > Replace spin_lock_irqsave by spin_lock.
> > 
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > ---
> >  kernel/irq/manage.c |    4 ++--
> >  1 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> > index ed7c5e3..6e9baf8 100644
> > --- a/kernel/irq/manage.c
> > +++ b/kernel/irq/manage.c
> > @@ -905,7 +905,7 @@ static void do_hardirq(struct irq_desc *desc)
> >  {
> >  	unsigned long flags;
> 
> Can flags be removed too?


Actually... I cheated.
Once the two patches were done, I saw the unused variable warning. So I remade the second patch
to remove flags but..yes it should be on the first patch, I must confess...
   
> > -	spin_lock_irqsave(&desc->lock, flags);
> > +	spin_lock(&desc->lock);
> >  
> >  	if (!(desc->status & IRQ_INPROGRESS))
> >  		goto out;
> > @@ -921,7 +921,7 @@ static void do_hardirq(struct irq_desc *desc)
> >  	else
> >  		thread_do_irq(desc);
> >   out:
> > -	spin_unlock_irqrestore(&desc->lock, flags);
> > +	spin_unlock(&desc->lock);
> >  
> >  	if (waitqueue_active(&desc->wait_for_handler))
> >  		wake_up(&desc->wait_for_handler);

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