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From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: Quick review of -rt RCU-related patches
Date: Wed, 05 Oct 2011 00:12:35 +0200	[thread overview]
Message-ID: <1317766355.32543.38.camel@twins> (raw)
In-Reply-To: <alpine.LFD.2.02.1110042322450.18778@ionos>

On Wed, 2011-10-05 at 00:05 +0200, Thomas Gleixner wrote:
> > peter_zijlstra-frob-rcu.patch
> > 
> >       Looks OK.  Hmmm...  Should this one go to mainline?
> >       Oh, looks equivalent, actually.  So why the change?
> 
> Peter ? 

-       if (in_irq() || in_serving_softirq()) {
+       if (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET)) {


For !rt its equivalent yes, for rt otoh its not:

int in_serving_softirq(void)
{
        int res;

        preempt_disable();
        res = __get_cpu_var(local_softirq_runner) == current;
        preempt_enable();
        return res;
}

However invoke_softirq() will still add SOFTIRQ_OFFSET so we need to
look at that to avoid recursion issues.

The changelog describes this. So this change is a direct consequence of
-rt frobbing the softirq stuff and thus isn't needed upstream. 

  reply	other threads:[~2011-10-04 22:13 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-10-04 17:47 Quick review of -rt RCU-related patches Paul E. McKenney
2011-10-04 22:05 ` Thomas Gleixner
2011-10-04 22:12   ` Peter Zijlstra [this message]
2011-10-04 23:15     ` Paul E. McKenney
2011-10-04 22:13   ` Peter Zijlstra
2011-10-04 23:15   ` Paul E. McKenney
2011-10-04 23:27     ` Thomas Gleixner
2011-10-04 23:56       ` Paul E. McKenney

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