Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763905AbYBTOVQ (ORCPT ); Wed, 20 Feb 2008 09:21:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763328AbYBTOU4 (ORCPT ); Wed, 20 Feb 2008 09:20:56 -0500 Received: from wr-out-0506.google.com ([64.233.184.235]:46697 "EHLO wr-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763303AbYBTOUx (ORCPT ); Wed, 20 Feb 2008 09:20:53 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=MjLJDG261QaxLD9Rj3vikhsTHKrtiPbi5/DqEHXLpnOKxLib/5OZCdRJBmpLH7h73IKFtZei78WvoIlZSfLfqquqfhMlGLPGNbnV91XngZ+5lXqhaetWzmd8GDdhp+13VgNLBg4ASXnbohcnj1J25yLPRmz7Ij4T2S8LqGuMeoc= Message-ID: Date: Wed, 20 Feb 2008 15:20:52 +0100 From: "Dmitry Adamushko" To: "Ahmed S. Darwish" Subject: Re: [PATCH] Tasklets: Avoid duplicating __tasklet_{,hi_}schedule() code Cc: "Ingo Molnar" , LKML In-Reply-To: <20080220133718.GA8205@ubuntu> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080219153720.GA2967@ubuntu> <20080219155252.GA27280@elte.hu> <20080219162718.GA3372@ubuntu> <20080220104113.GI3881@elte.hu> <20080220133718.GA8205@ubuntu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2393 Lines: 59 On 20/02/2008, Ahmed S. Darwish wrote: > On Wed, Feb 20, 2008 at 11:41:13AM +0100, Ingo Molnar wrote: > > > > * Ahmed S. Darwish 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. > > > > While we are at it, there's a small question that is bothering me > for a while (and I'm really thankful for help). > > I keep reading that softirqs (and naturally, tasklets) got executed > in interrupt context at the return from hardirq code path. > > Checking entry_32.S, I find no mentioning of softirqs on the return > path (beginning from ret_from_intr: to restore_all: ) > > The only invocation I'm able to find is from local_bh_enable() and > from ksoftirqd/n threads (by calling do_softirq()). AFAIK, both > invocations occur in a _nont-interrupt_ context (exception context). > > So, where does the interrupt-context tasklets invocation really > occur ? Look at irq_exit() in softirq.c. The common sequence is ... -> do_IRQ() --> irq_exit() --> invoke_softirq() -- Best regards, Dmitry Adamushko -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/