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=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 9B869C31E5B for ; Tue, 18 Jun 2019 00:44:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7B84020663 for ; Tue, 18 Jun 2019 00:44:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726778AbfFRAoE (ORCPT ); Mon, 17 Jun 2019 20:44:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52278 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726047AbfFRAoD (ORCPT ); Mon, 17 Jun 2019 20:44:03 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A6764308421A; Tue, 18 Jun 2019 00:44:03 +0000 (UTC) Received: from xz-x1.redhat.com (unknown [10.66.60.170]) by smtp.corp.redhat.com (Postfix) with ESMTP id 54DF41001DE7; Tue, 18 Jun 2019 00:43:57 +0000 (UTC) From: Peter Xu To: linux-kernel@vger.kernel.org Cc: Marcelo Tosatti , Luiz Capitulino , peterx@redhat.com, Thomas Gleixner Subject: [PATCH] timer: document TIMER_PINNED Date: Tue, 18 Jun 2019 08:43:56 +0800 Message-Id: <20190618004356.10357-1-peterx@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Tue, 18 Jun 2019 00:44:03 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The flag is very easy to understand but the interface is not, especially the assumption that add_timer_on() must be used to guarantee a correct behavior. For example, currently if we setup a pinned timer but later on we call mod_timer() upon the pinned timer, the mod_timer() will still try to run the timer on the current processor and migrate the timer if necessary. In other words, the suggested way to arm a pinned timer should be add_timer_on() always. mod_timer() can be used in this case only if current processor is the one that we want to pin the timer on. Document it a bit with the definition of TIMER_PINNED so that all future users will use it correctly. CC: Thomas Gleixner CC: linux-kernel@vger.kernel.org Signed-off-by: Peter Xu --- include/linux/timer.h | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/include/linux/timer.h b/include/linux/timer.h index 7b066fd38248..4a3408a05f86 100644 --- a/include/linux/timer.h +++ b/include/linux/timer.h @@ -36,19 +36,26 @@ struct timer_list { #define __TIMER_LOCKDEP_MAP_INITIALIZER(_kn) #endif -/* - * A deferrable timer will work normally when the system is busy, but - * will not cause a CPU to come out of idle just to service it; instead, - * the timer will be serviced when the CPU eventually wakes up with a - * subsequent non-deferrable timer. +/** + * @TIMER_DEFERRABLE: A deferrable timer will work normally when the + * system is busy, but will not cause a CPU to come out of idle just + * to service it; instead, the timer will be serviced when the CPU + * eventually wakes up with a subsequent non-deferrable timer. * - * An irqsafe timer is executed with IRQ disabled and it's safe to wait for - * the completion of the running instance from IRQ handlers, for example, - * by calling del_timer_sync(). + * @TIMER_IRQSAFE: An irqsafe timer is executed with IRQ disabled and + * it's safe to wait for the completion of the running instance from + * IRQ handlers, for example, by calling del_timer_sync(). * * Note: The irq disabled callback execution is a special case for * workqueue locking issues. It's not meant for executing random crap * with interrupts disabled. Abuse is monitored! + * + * @TIMER_PINNED: A pinned timer will not be affected by timer + * migration so it will always be run on a static cpu that was + * specified. Note: neither timer_setup() nor mod_timer() will + * guarantee correct pinning of timers. One should always use + * add_timer_on() when arm the timer to guarantee that the timer will + * be pinned to the target CPU correctly. */ #define TIMER_CPUMASK 0x0003FFFF #define TIMER_MIGRATING 0x00040000 -- 2.17.1