From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934604AbdKBWRm (ORCPT ); Thu, 2 Nov 2017 18:17:42 -0400 Received: from mx2.suse.de ([195.135.220.15]:57286 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934421AbdKBWRk (ORCPT ); Thu, 2 Nov 2017 18:17:40 -0400 Subject: Re: [PATCH v3] printk: Add console owner and waiter logic to load balance console writes To: Steven Rostedt , LKML , Peter Zijlstra Cc: akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang , Dave Hansen , Johannes Weiner , Mel Gorman , Michal Hocko , Petr Mladek , Sergey Senozhatsky , "yuwang.yuwang" , Linus Torvalds , Jan Kara , Mathieu Desnoyers , Tetsuo Handa References: <20171102134515.6eef16de@gandalf.local.home> From: Vlastimil Babka Message-ID: <82a3df5e-c8ad-dc41-8739-247e5034de29@suse.cz> Date: Thu, 2 Nov 2017 23:16:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171102134515.6eef16de@gandalf.local.home> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/02/2017 06:45 PM, Steven Rostedt wrote: ...> __DEVKMSG_LOG_BIT_ON = 0, > __DEVKMSG_LOG_BIT_OFF, > @@ -1753,8 +1760,56 @@ asmlinkage int vprintk_emit(int facility > * semaphore. The release will print out buffers and wake up > * /dev/kmsg and syslog() users. > */ > - if (console_trylock()) > + if (console_trylock()) { > console_unlock(); > + } else { > + struct task_struct *owner = NULL; > + bool waiter; > + bool spin = false; > + > + printk_safe_enter_irqsave(flags); > + > + raw_spin_lock(&console_owner_lock); > + owner = READ_ONCE(console_owner); > + waiter = READ_ONCE(console_waiter); > + if (!waiter && owner && owner != current) { > + WRITE_ONCE(console_waiter, true); > + spin = true; > + } > + raw_spin_unlock(&console_owner_lock); > + > + /* > + * If there is an active printk() writing to the > + * consoles, instead of having it write our data too, > + * see if we can offload that load from the active > + * printer, and do some printing ourselves. > + * Go into a spin only if there isn't already a waiter > + * spinning, and there is an active printer, and > + * that active printer isn't us (recursive printk?). > + */ > + if (spin) { > + /* We spin waiting for the owner to release us */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); > + /* Owner will clear console_waiter on hand off */ > + while (!READ_ONCE(console_waiter)) This should not be negated, right? We should spin while it's true, not false. > + cpu_relax(); > + > + spin_release(&console_owner_dep_map, 1, _THIS_IP_); > + printk_safe_exit_irqrestore(flags); > + > + /* > + * The owner passed the console lock to us. > + * Since we did not spin on console lock, annotate > + * this as a trylock. Otherwise lockdep will > + * complain. > + */ > + mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_); > + console_unlock(); > + printk_safe_enter_irqsave(flags); > + } > + printk_safe_exit_irqrestore(flags); > + > + } > } From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 1FE496B0038 for ; Thu, 2 Nov 2017 18:17:44 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id l23so1090573pgc.10 for ; Thu, 02 Nov 2017 15:17:44 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id n10si2602426plp.726.2017.11.02.15.17.42 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 02 Nov 2017 15:17:42 -0700 (PDT) Subject: Re: [PATCH v3] printk: Add console owner and waiter logic to load balance console writes References: <20171102134515.6eef16de@gandalf.local.home> From: Vlastimil Babka Message-ID: <82a3df5e-c8ad-dc41-8739-247e5034de29@suse.cz> Date: Thu, 2 Nov 2017 23:16:16 +0100 MIME-Version: 1.0 In-Reply-To: <20171102134515.6eef16de@gandalf.local.home> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Steven Rostedt , LKML , Peter Zijlstra Cc: akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang , Dave Hansen , Johannes Weiner , Mel Gorman , Michal Hocko , Petr Mladek , Sergey Senozhatsky , "yuwang.yuwang" , Linus Torvalds , Jan Kara , Mathieu Desnoyers , Tetsuo Handa On 11/02/2017 06:45 PM, Steven Rostedt wrote: ...> __DEVKMSG_LOG_BIT_ON = 0, > __DEVKMSG_LOG_BIT_OFF, > @@ -1753,8 +1760,56 @@ asmlinkage int vprintk_emit(int facility > * semaphore. The release will print out buffers and wake up > * /dev/kmsg and syslog() users. > */ > - if (console_trylock()) > + if (console_trylock()) { > console_unlock(); > + } else { > + struct task_struct *owner = NULL; > + bool waiter; > + bool spin = false; > + > + printk_safe_enter_irqsave(flags); > + > + raw_spin_lock(&console_owner_lock); > + owner = READ_ONCE(console_owner); > + waiter = READ_ONCE(console_waiter); > + if (!waiter && owner && owner != current) { > + WRITE_ONCE(console_waiter, true); > + spin = true; > + } > + raw_spin_unlock(&console_owner_lock); > + > + /* > + * If there is an active printk() writing to the > + * consoles, instead of having it write our data too, > + * see if we can offload that load from the active > + * printer, and do some printing ourselves. > + * Go into a spin only if there isn't already a waiter > + * spinning, and there is an active printer, and > + * that active printer isn't us (recursive printk?). > + */ > + if (spin) { > + /* We spin waiting for the owner to release us */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); > + /* Owner will clear console_waiter on hand off */ > + while (!READ_ONCE(console_waiter)) This should not be negated, right? We should spin while it's true, not false. > + cpu_relax(); > + > + spin_release(&console_owner_dep_map, 1, _THIS_IP_); > + printk_safe_exit_irqrestore(flags); > + > + /* > + * The owner passed the console lock to us. > + * Since we did not spin on console lock, annotate > + * this as a trylock. Otherwise lockdep will > + * complain. > + */ > + mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_); > + console_unlock(); > + printk_safe_enter_irqsave(flags); > + } > + printk_safe_exit_irqrestore(flags); > + > + } > } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org