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=-5.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 23F47C2D0E2 for ; Thu, 24 Sep 2020 08:54:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CDAA423787 for ; Thu, 24 Sep 2020 08:54:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="NPezC9Qd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727336AbgIXIyt (ORCPT ); Thu, 24 Sep 2020 04:54:49 -0400 Received: from mx2.suse.de ([195.135.220.15]:36166 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727287AbgIXIyr (ORCPT ); Thu, 24 Sep 2020 04:54:47 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1600937685; 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=Gnupa/FLLl5BSc73ruXnxSmNk2cnUZqVStpXpBHlSG8=; b=NPezC9QdftkpIrnAMch7/Gy7kMVeJhInMg8bpApfN7KFE0oNMe+k0ReKvOTPO/sW8KPEO8 9pGc7ShExvqmDy6iNhP84GbFjbYzMrnXkBZs7Zjnv7CCTp/X2ly20sNPAtXuAcEZ/KgGB7 w+sBMUijR6BI4MqCAydIP5CK1Ng6nzY= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id AA9B0ABF4; Thu, 24 Sep 2020 08:55:23 +0000 (UTC) Date: Thu, 24 Sep 2020 10:54:45 +0200 From: Petr Mladek To: Sergey Senozhatsky Cc: John Ogness , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Greg Kroah-Hartman , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH printk 3/5] printk: use buffer pool for sprint buffers Message-ID: <20200924085445.GK6442@alley> References: <20200922153816.5883-1-john.ogness@linutronix.de> <20200922153816.5883-4-john.ogness@linutronix.de> <20200924061746.GF577@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200924061746.GF577@jagdpanzerIV.localdomain> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2020-09-24 15:17:46, Sergey Senozhatsky wrote: > On (20/09/22 17:44), John Ogness wrote: > > +/* > > + * The sprint buffers are used with interrupts disabled, so each CPU > > + * only requires 2 buffers: for non-NMI and NMI contexts. Recursive > > + * printk() calls are handled by the safe buffers. > > + */ > > +#define SPRINT_CTX_DEPTH 2 > > + > > +/* Static sprint buffers for early boot (only 1 CPU). */ > > +static DECLARE_BITMAP(sprint_static_textbuf_map, SPRINT_CTX_DEPTH); > > +static char sprint_static_textbuf[SPRINT_CTX_DEPTH * LOG_LINE_MAX]; > > + > > +/* Dynamically allocated sprint buffers. */ > > +static unsigned int sprint_dynamic_textbuf_count; > > +static unsigned long *sprint_dynamic_textbuf_map; > > +static char *sprint_dynamic_textbuf; > > Just a question: > > Can dynamic_textbuf be a PER_CPU array of five textbuf[1024] buffers > (for normal printk, nmi, hard irq, soft irq and one extra buffer for > recursive printk calls)? That would be my preferred fallback when the approach with vsprintf(NULL, ) is not acceptable for some reasons. But I still think that calling vsprintf(NULL, ) is the most trivial and good enough solution. IMHO, the solution with per-CPU buffers is not that trivial, for example: What if recursive printk() is interrupted by NMI and it causes yet another recursion? Is one level of recursion enough? Best Regards, Petr