From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 56B41C433FE for ; Wed, 30 Nov 2022 16:10:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230129AbiK3QKg (ORCPT ); Wed, 30 Nov 2022 11:10:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60902 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230136AbiK3QKb (ORCPT ); Wed, 30 Nov 2022 11:10:31 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6AB9D490B9; Wed, 30 Nov 2022 08:10:30 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id EA4A761CC7; Wed, 30 Nov 2022 16:10:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 85091C433D6; Wed, 30 Nov 2022 16:10:28 +0000 (UTC) Date: Wed, 30 Nov 2022 11:10:26 -0500 From: Steven Rostedt To: Daniel Bristot de Oliveira Cc: Masami Hiramatsu , Jonathan Corbet , Juri Lelli , Clark Williams , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V3 2/3] tracing/osnoise: Add preempt/irq disable options Message-ID: <20221130111026.47b9c456@gandalf.local.home> In-Reply-To: <700e7f91-00a9-d625-741d-122b9b1e1e1c@kernel.org> References: <03d4a8522792fa3a51920c79f8a5074933a2fcb3.1669409262.git.bristot@kernel.org> <20221128153919.33c008d1@gandalf.local.home> <700e7f91-00a9-d625-741d-122b9b1e1e1c@kernel.org> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, 30 Nov 2022 16:47:29 +0100 Daniel Bristot de Oliveira wrote: > On 11/28/22 21:39, Steven Rostedt wrote: > > On Fri, 25 Nov 2022 22:20:23 +0100 > > Daniel Bristot de Oliveira wrote: > > > >> @@ -1308,6 +1315,8 @@ static void notify_new_max_latency(u64 latency) > >> */ > >> static int run_osnoise(void) > >> { > >> + bool preempt_disable = test_bit(OSN_PREEMPT_DISABLE, &osnoise_options); > >> + bool irq_disable = test_bit(OSN_IRQ_DISABLE, &osnoise_options); > > > > bool irq_disable = test_bit(OSN_IRQ_DISABLE, &osnoise_options); > > bool preempt_disable = IS_ENABLED(CONFIG_PREEMPT) && > > !irq_disable && test_bit(OSN_PREEMPT_DISABLE, &osnoise_options); > > Ooops again, that is not exactly what I wanted, because... Then just remove the "IS_ENABLED()" part and it should work just fine. > > >> struct osnoise_variables *osn_var = this_cpu_osn_var(); > >> u64 start, sample, last_sample; > >> u64 last_int_count, int_count; > >> @@ -1335,6 +1344,14 @@ static int run_osnoise(void) > >> */ > >> threshold = tracing_thresh ? : 5000; > >> > >> + /* > >> + * IRQ disable also implies in preempt disable. > >> + */ > >> + if (irq_disable) > >> + local_irq_disable(); > > > > if (preempt_disable) > >> + preempt_disable(); The above is a nop when CONFIG_PREEMPT is false. > >> + > >> /* > >> * Make sure NMIs see sampling first > >> */ > >> @@ -1422,16 +1439,21 @@ static int run_osnoise(void) > >> * cond_resched() > >> */ > >> if (IS_ENABLED(CONFIG_PREEMPT_RCU)) { > >> - local_irq_disable(); > >> + if (!irq_disable) > >> + local_irq_disable(); > >> + > >> rcu_momentary_dyntick_idle(); > >> - local_irq_enable(); > >> + > >> + if (!irq_disable) > >> + local_irq_enable(); > >> } > >> > >> /* > >> * For the non-preemptive kernel config: let threads runs, if > >> - * they so wish. > >> + * they so wish, unless set not do to so. > >> */ > > Then I end up cond_resched'ing here in the non-preemptive kernel. Sorry, I missed the point that you want to *not* cond_resched() even in a CONFIG_PREEMPT is false situation, if preempt_disable flag is set. That's the reason I added the IS_ENABLED(CONFIG_PREEMPT) check at the top. I originally didn't have that, but then thought this should always happen in that case. > > >> - cond_resched(); > >> + if (!irq_disable && !preempt_disable) > >> + cond_resched(); > > But I also want to avoid this cond_resched if preempt_disable is set. Right, so just remove the IS_ENABLED() part in the beginning. > > So, I will merge both things: > > - change the preempt_disable assignment to check !irq_disabled, like: > > /* > * Disabling preemption is only required if IRQs are enabled, and the options is set on. > */ > preempt_disable = !irq_disable && test_bit(OSN_PREEMPT_DISABLE, &osnoise_options); Yep (that's what I original had until I changed it) > > - change the preempt disabled if to > if (IS_ENABLED(CONFIG_PREEMPT) && preempt_disabled) > preempt_disable(); No need, preempt_disable() is a nop when CONFIG_PREEMPT is false. > > I tested with both preemption models (preemptive and not preemptive) and it works fine. > > am I missing something? Just that you don't need to add the IS_ENABLED() part at all. -- Steve