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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 4C301ECDFBB for ; Fri, 20 Jul 2018 13:27:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C0DE020652 for ; Fri, 20 Jul 2018 13:27:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C0DE020652 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732152AbeGTOPo (ORCPT ); Fri, 20 Jul 2018 10:15:44 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:16365 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732136AbeGTOPn (ORCPT ); Fri, 20 Jul 2018 10:15:43 -0400 Received: from fsav102.sakura.ne.jp (fsav102.sakura.ne.jp [27.133.134.229]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w6KDRObg093699; Fri, 20 Jul 2018 22:27:24 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav102.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav102.sakura.ne.jp); Fri, 20 Jul 2018 22:27:24 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav102.sakura.ne.jp) Received: from [192.168.1.8] (softbank126074194044.bbtec.net [126.74.194.44]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w6KDRGvj093639 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 20 Jul 2018 22:27:24 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [RFC PATCH] sched/debug: Use terse backtrace for idly sleeping threads. To: Peter Zijlstra Cc: "James E.J. Bottomley" , "Martin K. Petersen" , Ingo Molnar , Thomas Gleixner , Tejun Heo , "Paul E. McKenney" , Andrew Morton , Dmitry Vyukov , linux-kernel@vger.kernel.org References: <1532007443-3538-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180719134653.GH2476@hirez.programming.kicks-ass.net> From: Tetsuo Handa Message-ID: <54fc7ab8-2995-e864-7f74-c4434d23622c@i-love.sakura.ne.jp> Date: Fri, 20 Jul 2018 22:27:17 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180719134653.GH2476@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/07/19 22:46, Peter Zijlstra wrote: > On Thu, Jul 19, 2018 at 10:37:23PM +0900, Tetsuo Handa wrote: >> This patch can be applied before proposing abovementioned changes. >> Since there are many kernel threads whose backtrace is boring due to idly >> waiting for an event inside the main loop, this patch introduces a kernel >> config option (which allows SysRq-t to use one-liner backtrace for threads >> idly waiting for an event) and simple helpers (which allow current thread >> to declare that current thread is about to start/end idly waiting). > >> diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c >> index f776807..6b8c8bd 100644 >> --- a/drivers/base/devtmpfs.c >> +++ b/drivers/base/devtmpfs.c >> @@ -406,7 +406,9 @@ static int devtmpfsd(void *p) >> } >> __set_current_state(TASK_INTERRUPTIBLE); >> spin_unlock(&req_lock); >> + start_idle_sleeping(); >> schedule(); >> + end_idle_sleeping(); >> } >> return 0; >> out: > > So I _really_ hate the idea of sprinking that all around the kernel like > this. > Does that comment mean the idea of "using one-liner backtrace for threads idly waiting for an event" itself is OK? Since there already is schedule_idle() function, introducing idly_schedule() etc. is very confusing. What I'm trying to do is to tell debug function that "I'm currently in neutral situation and hence dumping my backtrace will not give you interesting result". Since such section needs to be carefully annotated with comments, I think that lockdep-like annotation fits better than introducing wrapped functions.