linux-kernel - Re: [PATCH RT] convert RCU Preempt tasklet into softirq.

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Message-ID: <20070906180634.GG8030@linux.vnet.ibm.com>
Date:	Thu, 6 Sep 2007 11:06:34 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Clark Williams <williams@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	john stultz <johnstul@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...sign.ru>,
	LKML <linux-kernel@...r.kernel.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	RT <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH RT] convert RCU Preempt tasklet into softirq.

On Thu, Sep 06, 2007 at 12:52:00PM -0500, Clark Williams wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Paul E. McKenney wrote:
> > On Fri, Jun 08, 2007 at 03:43:48PM -0400, Steven Rostedt wrote:
> >> On Fri, 2007-06-08 at 12:36 -0700, Paul E. McKenney wrote:
> >>> On Fri, Jun 08, 2007 at 11:27:08AM -0400, Steven Rostedt wrote:
> >>>> The first time I compiled it, I forgot the ';' and got a warning there.
> >>>> But the warning also included "declaring structure softirq_action in
> >>>> prototype", so I fixed both the ';' and added the struct. I can try
> >>>> compile without it. But I also know that adding #include <interrupt.h>
> >>>> in rcupreempt.h caused issues too.
> >>> If I leave out both the "struct softirq_action" and the
> >>> rcu_process_callbacks() declaration,, it compiles for me.
> >>>
> >>> So I guess the rcu_process_callbacks() should be declared static...
> >> OK, I can update the patch to reflect that. Remember, I didn't learn
> >> anything from doing this patch, so I have no idea why
> >> rcu_procell_callbacks was global. I was just keeping to the norm. :-)
> > 
> > Hey, -I- learned something from your doing the patch -- namely that
> > rcu_process_callbacks() was needlessly non-static.  ;-)
> > 
> >> Actually, I'll make a separate patch for this change. This is a
> >> different issue.
> > 
> > Sounds good!
> > 
> 
> Paul,
> 
> I had a test run of a kernel using Steven's patch (RCU using tasklets) going over the
> weekend. It looks like it made it through running racer for 24hrs without a panic,
> but I'm not entirely convinced (since my reservation of the test system expired on
> Saturday and I didn't look at it until Wednesday; bad Clark, no doughnut).
> 
> I've got another test running now and I'll be able to poke around on the system
> tomorrow morning to see if in fact there were no RCU related Oops'en. I'll let you
> know what we find.

Thank you for the info, Clark!

Of course, this all begs the question of why the heck switching from
tasklets to softirqs should make any difference at all...

							Thanx, Paul
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