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 6DC8AC4332F for ; Fri, 4 Nov 2022 16:44:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230267AbiKDQoJ (ORCPT ); Fri, 4 Nov 2022 12:44:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37424 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231693AbiKDQnt (ORCPT ); Fri, 4 Nov 2022 12:43:49 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2DA0B31EF9 for ; Fri, 4 Nov 2022 09:43:48 -0700 (PDT) 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 ams.source.kernel.org (Postfix) with ESMTPS id DE9D4B82E72 for ; Fri, 4 Nov 2022 16:43:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0D007C433D6; Fri, 4 Nov 2022 16:43:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1667580225; bh=vrLFKGbB+WonWostWlSiKuz27yHax/ThgTlKqQVTgQc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kk5AVgkkcTwryvrh2TJfl7NM2BKytqTBHdEgOXT2xqFY+wl4POYrFfa4QAamr5vqb reNy8dz5iWRdgDjEpLGBavDGqCNLPvHf98qJIqxZCvG1kdEDXhz6RkpMar1Fdc88Up B+j5D1mZGSIg5QCWtZIN7/Fqh1+HtA4Q4/Ke18nBket/nuElg7fRMyDwiAx/ntwPDK IAKEICkjRbmYwqcvyU5o72UCKZqTeBYPGHavvVhSyyGHhEoXRdIx4fEnXHNqWfwmnr 4Ud4W72vgP2U1aitNzu9F//GNbqosFqagOixG5lRdJbos2UgFqpdBOmTtE53p4fIMI LRlMZH2v1QjJQ== Date: Fri, 4 Nov 2022 17:43:42 +0100 From: Frederic Weisbecker To: Anna-Maria Behnsen Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , John Stultz , Thomas Gleixner , Eric Dumazet , "Rafael J . Wysocki" , Arjan van de Ven , "Paul E . McKenney" , Frederic Weisbecker , Rik van Riel , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Theodore Ts'o , "Jason A. Donenfeld" , Stephen Boyd , Tejun Heo , Lai Jiangshan Subject: Re: [PATCH v4 05/16] add_timer_on(): Make sure callers have TIMER_PINNED flag Message-ID: <20221104164342.GA1440400@lothringen> References: <20221104145737.71236-1-anna-maria@linutronix.de> <20221104145737.71236-6-anna-maria@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221104145737.71236-6-anna-maria@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 04, 2022 at 03:57:26PM +0100, Anna-Maria Behnsen wrote: > The implementation of the hierachical timer pull model will change the > timer bases per CPU. Timers, that have to expire on a specific CPU, require > the TIMER_PINNED flag. Otherwise they will be queued on the dedicated CPU > but in global timer base and those timers could also expire on other > CPUs. Timers with TIMER_DEFERRABLE flag end up in a separate base anyway > and are executed on the local CPU only. > > Therefore add the missing TIMER_PINNED flag for those callers who use > add_timer_on() without the flag. No functional change. You're fixing the current callers but what about the future ones? add_timer_on() should always guarantee that a timer runs on the right destination, which is not the case after your patchset if the timer hasn't been set to TIMER_PINNED. Therefore I think we should either have: * add_timer_on() enforce TIMER_PINNED (doesn't work because if the timer is later called with mod_timer(), we should expect it to run anywhere) or * add_timer_on() warns if !TIMER_PINNED or * have an internal flag TIMER_LOCAL, that is turned on when add_timer_on() is called or add_timer()/mod_timer() is called on a TIMER_PINNED. Otherwise it is turned off. The last solution should work with existing API and you don't need to chase the current and future users of add_timer_on(). Thanks.