Re: [PATCH] Tasklets: Avoid duplicating __tasklet_{,hi_}schedule() code

From: Ingo Molnar <mingo@elte.hu>
To: "Ahmed S. Darwish" <darwish.07@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Tasklets: Avoid duplicating __tasklet_{,hi_}schedule() code
Date: Wed, 20 Feb 2008 11:41:13 +0100	[thread overview]
Message-ID: <20080220104113.GI3881@elte.hu> (raw)
In-Reply-To: <20080219162718.GA3372@ubuntu>

* Ahmed S. Darwish <darwish.07@gmail.com> wrote:

> > > -		local_irq_disable();
> > > -		t->next = __get_cpu_var(tasklet_vec).list;
> > > -		__get_cpu_var(tasklet_vec).list = t;
> > > -		__raise_softirq_irqoff(TASKLET_SOFTIRQ);
> > > -		local_irq_enable();
> > > +		/* We were not lucky enough to run, reschedule. */
> > > +		__tasklet_schedule(t);
> > 
> > i think there's a subtle difference that you missed: this one does 
> > __raise_softirq_irqoff(), while __tasklet_schedule() does a 
> > raise_softirq_irqoff(). (note the lack of undescores)
> > 
> > the reason is to avoid infinitely self-activating tasklets.
> 
> Indeed, thanks a lot for the explanation. (maybe it's time to check 
> for new eyeglasses ;)).

nah, it's rather subtle and the code looked good to me at first but i 
remembered that there was some small detail here to watch out for.

i really dont like tasklets due to their many, arbitrary scheduling 
limitations, we should really use the "turn tasklets into kthreads" 
patch i posted last year.

	Ingo