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=-0.4 required=3.0 tests=BUG6152_INVALID_DATE_TZ_ABSURD,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS,INVALID_DATE_TZ_ABSURD,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 00098C433DF for ; Wed, 1 Jul 2020 19:58:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF31220748 for ; Wed, 1 Jul 2020 19:58:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="VcccQpHI"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ElYBtgVa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726895AbgGAT6W (ORCPT ); Wed, 1 Jul 2020 15:58:22 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:42176 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725771AbgGAT6W (ORCPT ); Wed, 1 Jul 2020 15:58:22 -0400 X-Greylist: delayed 165618 seconds by postgrey-1.27 at vger.kernel.org; Wed, 01 Jul 2020 15:58:21 EDT From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1593633499; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=lT9zajvxSVCwKbbkbNiXXnFEejqxJREj9fDOL+2G3jc=; b=VcccQpHIsvg8wpMdxlOWoKrNzGvYmajmmFoLXjzZUKKQILCYVYE5LfRrogTRZ8dDCjlT01 BdjC+u2eH4lP+V1ra0QBZvUIeE50B9wQprM7isXv9dLDb47VJy9kNo9dQ/YUDGMkktOSSO tmhSuClHdemmm5KuiQI2gUDh6+Cuc8ryxcdxgkJgqd6eN2fzopIWXI1Qa4f8oDwLA9b4G2 SSGS9OVvxcMdrHp/AFW+pi+w1esuge7XuFWEwQBA6LYujcVDxPbTsE4W4M8UH50G6gvc6n 2y8BItFxCmEaaI+XIs2ya0nhNsZXRjO8JfDgxGZddjHdvn73MfEYoqawlW1FHA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1593633499; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=lT9zajvxSVCwKbbkbNiXXnFEejqxJREj9fDOL+2G3jc=; b=ElYBtgVaS13sLgg5ngPELxflDHtPZGxBeD5FSbUKtihCrm6sIu6rK4MGDil2f7nPyfYoGt MFMRr3WPSDkAf7CA== To: Petr Mladek Cc: Peter Zijlstra , Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Andrea Parri , Thomas Gleixner , Paul McKenney , kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: pending output optimization: was: [PATCH v3 3/3] printk: use the lockless ringbuffer In-Reply-To: <20200625151741.GH8444@alley> References: <20200618144919.9806-1-john.ogness@linutronix.de> <20200618144919.9806-4-john.ogness@linutronix.de> <20200625151741.GH8444@alley> Date: Wed, 01 Jul 2020 22:04:19 +0206 Message-ID: <87o8oznh2c.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-06-25, Petr Mladek wrote: >> --- a/kernel/printk/printk.c >> +++ b/kernel/printk/printk.c >> @@ -2009,9 +2056,9 @@ asmlinkage int vprintk_emit(int facility, int level, >> >> /* This stops the holder of console_sem just where we want him */ >> logbuf_lock_irqsave(flags); >> - curr_log_seq = log_next_seq; >> + pending_output = !prb_read_valid(prb, console_seq, NULL); >> printed_len = vprintk_store(facility, level, dict, dictlen, fmt, args); >> - pending_output = (curr_log_seq != log_next_seq); >> + pending_output &= prb_read_valid(prb, console_seq, NULL); > > This will stop working after we remove the locks. Consoles will be > able to handle messages while the new one is being added. There will > be no gurantee that someone is still hadling the previously pending > output. > > Please, always handle consoles when printed_len is not zero!!! > > The pending output was just an optimization added recently. Nobody > requested it. It was just an idea that made sense. OK. I will insert a patch before this one that reverts commit 3ac37a93fa92 ("printk: lock/unlock console only for new logbuf entries"). Then there is no @pending_output for me to implement and it will be clear that this series is changing/reverting some printk behavior. John Ogness