From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765959AbYBTTl5 (ORCPT ); Wed, 20 Feb 2008 14:41:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759325AbYBTTlq (ORCPT ); Wed, 20 Feb 2008 14:41:46 -0500 Received: from ug-out-1314.google.com ([66.249.92.173]:2737 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758376AbYBTTlo (ORCPT ); Wed, 20 Feb 2008 14:41:44 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:to:cc:subject:message-id:references:mime-version:content-type:content-disposition:in-reply-to:user-agent:from; b=wKH780WTnitzIZ7HQ46VcDgwos7PbNXInLixQdxo1gH5dfGJNwmRARdVyfmX9gu6jGTSB5UYiLah5kJH3vUU/BJ0JLPEczavPEKlRBEMz9tGpCteSBJ+wRqLIxNwaz+3y3a/D+LPJapE1VICGoh5kC3ough+GNVu5RzR2L4tS5E= Date: Wed, 20 Feb 2008 21:39:09 +0200 To: Dmitry Adamushko Cc: Ingo Molnar , LKML , Andrew Morton Subject: Re: [PATCH] Tasklets: Avoid duplicating __tasklet_{,hi_}schedule() code Message-ID: <20080220193909.GA6344@ubuntu> References: <20080219153720.GA2967@ubuntu> <20080219155252.GA27280@elte.hu> <20080219162718.GA3372@ubuntu> <20080220104113.GI3881@elte.hu> <20080220133718.GA8205@ubuntu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.15+20070412 (2007-04-11) From: "Ahmed S. Darwish" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 20, 2008 at 03:20:52PM +0100, Dmitry Adamushko wrote: > 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() > > Great, this was the last missing block in my understanding of softirqs :). Thank you. [btw, your MUA broke the CC list] -- Ahmed S. Darwish Homepage: http://darwish.07.googlepages.com Blog: http://darwish-07.blogspot.com