From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752572AbcHJVSB (ORCPT ); Wed, 10 Aug 2016 17:18:01 -0400 Received: from mail-yw0-f194.google.com ([209.85.161.194]:35251 "EHLO mail-yw0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752425AbcHJVR5 (ORCPT ); Wed, 10 Aug 2016 17:17:57 -0400 MIME-Version: 1.0 In-Reply-To: <20160406082758.GA3554@quack.suse.cz> References: <1459789048-1337-1-git-send-email-sergey.senozhatsky@gmail.com> <1459789048-1337-2-git-send-email-sergey.senozhatsky@gmail.com> <20160404155149.a3e3307def2d1315e2099c63@linux-foundation.org> <20160406082758.GA3554@quack.suse.cz> From: Viresh Kumar Date: Wed, 10 Aug 2016 14:17:55 -0700 X-Google-Sender-Auth: 9DDKU1wr9gZrPoDMT4XEAUyGxhk Message-ID: Subject: Re: [PATCH v10 1/2] printk: Make printk() completely async To: Jan Kara , Andrew Morton , Sergey Senozhatsky Cc: Jan Kara , Petr Mladek , Tejun Heo , Tetsuo Handa , "linux-kernel@vger.kernel.org" , Byungchul Park , Sergey Senozhatsky , vlevenetz@mm-sol.com, Greg Kroah-Hartman Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org +Vladi/Greg, On Wed, Apr 6, 2016 at 1:27 AM, Jan Kara wrote: > On Mon 04-04-16 15:51:49, Andrew Morton wrote: >> > +static int __init init_printk_kthread(void) >> > +{ >> > + struct task_struct *thread; >> > + >> > + if (printk_sync) >> > + return 0; >> > + >> > + thread = kthread_run(printk_kthread_func, NULL, "printk"); >> >> This gets normal scheduling policy, so a spinning userspace SCHED_FIFO >> task will block printk for ever. This seems bad. > > I have to research this a bit but won't the SCHED_FIFO task that has > potentially unbounded amount of work lockup the CPU even though it does > occasional cond_resched()? We are facing complete hogs because of the printk thread being a SCHED_FIFO task and have this patch to fix it up for now. Author: Vladislav Levenetz Date: Wed Aug 10 13:58:00 2016 -0700 SW-7786: printk: Lower the priority of printk thread Flooding the console (with a test module) in a tight loop indefinitely makes android user interface very sluggish. Opening YouTube app and the device hangs and becomes even more unresponsive to the point it completely hangs. The asynchronous printk thread is a SCHED FIFO thread with priority MAX_RT_PRIO - 1. If we create it as a simple thread (i.e. no SCHED FIFO) instead, we observe much better performance using the same printk flood test. We don't even notice any kind of sluggishness during device usage. We can play a YouTube clip smoothly and use the device normally in general. The kernel log looks fine as well, as the flood of messages continue normally. Signed-off-by: Vladislav Levenetz Signed-off-by: Viresh Kumar --- kernel/printk/printk.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index c32872872cb6..ad5b30e5e6d9 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2856,9 +2856,6 @@ static int printk_kthread_func(void *data) static int __init_printk_kthread(void) { struct task_struct *thread; - struct sched_param param = { - .sched_priority = MAX_RT_PRIO - 1, - }; if (!printk_kthread_can_run || printk_sync || printk_kthread) return 0; @@ -2870,7 +2867,6 @@ static int __init_printk_kthread(void) return PTR_ERR(thread); } - sched_setscheduler(thread, SCHED_FIFO, ¶m); printk_kthread = thread; return 0; }