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 44950C49EA3 for ; Sat, 19 Jun 2021 08:23:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 22A9B61222 for ; Sat, 19 Jun 2021 08:23:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234209AbhFSIY4 (ORCPT ); Sat, 19 Jun 2021 04:24:56 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:33242 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233963AbhFSIYz (ORCPT ); Sat, 19 Jun 2021 04:24:55 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1624090963; 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=v+U7odfbFJQovsecU7GWc8bZHX2YJeBH6Eg6K0NB8gM=; b=Fl+4IBB7n1c5fEc3KsVVeFX1RJWuf5GmifPMiOVdfYCjDLA5KCv+ZKyHrpGoiYKnW40/H8 00tnO18BD7BQGnZtLkH9Z/yo8Eduu1mh4GX0Nhj5GsWDY0+y2D7snLgaiMd1oz5Iuuw+pB 1/OSMpdPHD2jSCPwRyXPY/pVGQpIJtSWkbqrrrx9fv7WDVtaZH1XZHDgmJRTlxL8UUBuBK yNqNvEtewQiD1m/GscZaMAJkf1BfgrqG+hVuieodxwL1S2Tppf530XIRcF3Sc7Qbb/3MjD iv7JqVcMJGwruWXoWH22bILXrp0qOMPymz874eVxwEHNQrXVNqLCzKaiMLQLIA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1624090963; 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=v+U7odfbFJQovsecU7GWc8bZHX2YJeBH6Eg6K0NB8gM=; b=TKZd+OX6JDIsX7c0GvSmeNjKLCmA1+djgPZB5Q3kS5vK8B1UzDR1A6jsGHQvPfLH3cTDLq RopOStLAQUaM5KBQ== To: Nicolas Saenz Julienne Cc: linux-rt-users@vger.kernel.org, frederic@kernel.org, mtosatti@redhat.com, LKML , Peter Zijlstra Subject: Re: [RFC 2/2] timers: Make sure irq_work is handled when no pending timers In-Reply-To: <87mtrmeqon.ffs@nanos.tec.linutronix.de> References: <20210610125945.558872-1-nsaenzju@redhat.com> <20210610125945.558872-2-nsaenzju@redhat.com> <87mtrmeqon.ffs@nanos.tec.linutronix.de> Date: Sat, 19 Jun 2021 10:22:43 +0200 Message-ID: <875yyae018.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jun 19 2021 at 00:47, Thomas Gleixner wrote: > On Thu, Jun 10 2021 at 14:59, Nicolas Saenz Julienne wrote: > As we since then made work queues RT aware and it's possible to queue > work from the irq_work IPI context, the obvious solution is to delegate > this to a work queue. > > If we do a proper analysis of the affected irq work callbacks then this > probably makes a lot of sense independent of RT. There are only a few > really urgent irq work items which need to be handled immediately in the > IPI. > > RT is special, but as we have demonstrated over time it's not _that_ > special. It just needs a proper analysis and a real good argument why > something has to be special for RT and does not fit into the common > case. Or to demonstrate that the common case approach of 'do it right > away' is pointless or even harmfull. I skimmed most of the ~40 irq_work instances. Most of them have no urgency at all. And out of those non-urgent cases the majority does not even have the requirement to run on the current CPU, so they can be pushed off to a global work queue which moves them away from NOHZ full CPUs completely. That has nothing to do with RT, that's a benefit in general. Thanks, tglx