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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BFA3AC433ED for ; Tue, 13 Apr 2021 08:39:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95E79613B2 for ; Tue, 13 Apr 2021 08:39:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230117AbhDMIkD (ORCPT ); Tue, 13 Apr 2021 04:40:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229891AbhDMIkB (ORCPT ); Tue, 13 Apr 2021 04:40:01 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A1F34C061574; Tue, 13 Apr 2021 01:39:42 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1618303179; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=jH35UaKzKxFZTz+38gYIJANUU3Yo7Uur7vXQ1BzIgEk=; b=37o11+IJE6Kv3tz9VF5qjnqquXxAfDHUO2RR9dU9Xpmux/tJ1Ya0O/6QW6CUKYlUmUuki1 yk6x5sCVYp2RE1qlZcIWXcXGqQDfqE6b9rofrEF1l4W9Bu0lQYPIOfrpp5EWCLyhuzoDKR noJFMLkdFwDHrZWh28dwY/D+ZLSb1kOl99Kr6aho0kZM/kJh+fV7SUV11cUs7VJmthm7UL AKwn9TvznInOZS8mMQW5TSE32SUcLDuiqiTY/lb3bdlnpMtoo3M4f5FisV70sLN19VaPqS CVZfdO4qHaiQJkI5PACVS5nXdWpseYGJ/CwRFLo7HhhKZaZyKXUfOXeYwTSDOA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1618303179; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=jH35UaKzKxFZTz+38gYIJANUU3Yo7Uur7vXQ1BzIgEk=; b=011t0SOknZVZ53KQHSyhMVFCxDt2tni3dqjnWNlIRFKqqHWC7xqzL5Cma/5WgHzAiCEXjC 0oTt35aK0c0TSTBg== To: Song Chen Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, keescook@chromium.org, gregkh@linuxfoundation.org, maz@kernel.org, joe@perches.com, romain.perier@gmail.com, john.garry@huawei.com Subject: Re: [PATCH] kernel:irq:manage: request threaded irq with a specified priority In-Reply-To: <1618294774-24370-1-git-send-email-chensong_2000@189.cn> References: <1618294774-24370-1-git-send-email-chensong_2000@189.cn> Date: Tue, 13 Apr 2021 10:39:39 +0200 Message-ID: <875z0qzigk.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Tue, Apr 13 2021 at 14:19, Song Chen wrote: > In general, irq handler thread will be assigned a default priority which > is MAX_RT_PRIO/2, as a result, no one can preempt others. > > Here is the case I found in a real project, an interrupt int_a is > coming, wakes up its handler handler_a and handler_a wakes up a > userspace RT process task_a. > > However, if another irq handler handler_b which has nothing to do > with any RT tasks is running when int_a is coming, handler_a can't > preempt handler_b, as a result, task_a can't be waken up immediately > as expected until handler_b gives up cpu voluntarily. In this case, > determinism breaks. It breaks because the system designer failed to assign proper priorities to the irq threads int_a, int_b and to the user space process task_a. That's not solvable at the kernel level. Thanks, tglx