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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 D9EA8C433ED for ; Thu, 6 May 2021 08:00:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98EEA61008 for ; Thu, 6 May 2021 08:00:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233663AbhEFIBZ (ORCPT ); Thu, 6 May 2021 04:01:25 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:17471 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233565AbhEFIBY (ORCPT ); Thu, 6 May 2021 04:01:24 -0400 Received: from DGGEMS404-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4FbQt61WgMzkWpZ; Thu, 6 May 2021 15:57:50 +0800 (CST) Received: from huawei.com (10.69.192.56) by DGGEMS404-HUB.china.huawei.com (10.3.19.204) with Microsoft SMTP Server id 14.3.498.0; Thu, 6 May 2021 16:00:18 +0800 From: Luo Jiaxing To: , , , CC: , , , Subject: [PATCH] printk: stop spining waiter when console resume to flush prb Date: Thu, 6 May 2021 16:00:26 +0800 Message-ID: <1620288026-5373-1-git-send-email-luojiaxing@huawei.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.69.192.56] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Some threads still call printk() for printing when resume_console() is being executed. In practice, the printk() is executed for a period of time and then returned. The duration is determined by the number of prints cached in the prb during the suspend/resume process. At the same time, resume_console() returns quickly. Base on owner/waiter machanism, the frist one who fail to lock console will become waiter, and start spining. When current owner finish print one informance, if a waiter is waitting, owner will give up and let waiter become a new owner. New owner need to flush the whole prb unitl prb empty or another new waiter come and take the job from him. So the first waiter after resume_console() will take seconds to help to flush prb, but driver which call printk() may be bothered by this. New a flag to mark resume flushing prb. When the console resume, before the prb is empty, stop to set a new waiter temporarily. Signed-off-by: Luo Jiaxing --- kernel/printk/printk.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 575a34b..2c680a5 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -287,6 +287,9 @@ EXPORT_SYMBOL(console_set_on_cmdline); /* Flag: console code may call schedule() */ static int console_may_schedule; +/* Flags: console flushing prb when resume */ +static atomic_t console_resume_flush_prb = ATOMIC_INIT(0); + enum con_msg_format_flags { MSG_FORMAT_DEFAULT = 0, MSG_FORMAT_SYSLOG = (1 << 0), @@ -1781,7 +1784,8 @@ static int console_trylock_spinning(void) raw_spin_lock(&console_owner_lock); owner = READ_ONCE(console_owner); waiter = READ_ONCE(console_waiter); - if (!waiter && owner && owner != current) { + if (!waiter && owner && owner != current && + !atomic_read(&console_resume_flush_prb)) { WRITE_ONCE(console_waiter, true); spin = true; } @@ -2355,6 +2359,7 @@ void resume_console(void) if (!console_suspend_enabled) return; down_console_sem(); + atomic_set(&console_resume_flush_prb, 1); console_suspended = 0; console_unlock(); } @@ -2592,6 +2597,8 @@ void console_unlock(void) raw_spin_unlock(&logbuf_lock); up_console_sem(); + if (atomic_read(&console_resume_flush_prb)) + atomic_set(&console_resume_flush_prb, 0); /* * Someone could have filled up the buffer again, so re-check if there's -- 2.7.4