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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,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 9FEE3C433DF for ; Fri, 10 Jul 2020 08:43:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6C3952078D for ; Fri, 10 Jul 2020 08:43:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="g2s1CDwY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726921AbgGJInJ (ORCPT ); Fri, 10 Jul 2020 04:43:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46672 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726768AbgGJInI (ORCPT ); Fri, 10 Jul 2020 04:43:08 -0400 Received: from mail-pj1-x1043.google.com (mail-pj1-x1043.google.com [IPv6:2607:f8b0:4864:20::1043]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 90981C08C5CE for ; Fri, 10 Jul 2020 01:43:08 -0700 (PDT) Received: by mail-pj1-x1043.google.com with SMTP id b92so2308347pjc.4 for ; Fri, 10 Jul 2020 01:43:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=hhtnEx6dVeh1pIqAmosCNZhZcA/Z3fpbgOYNTfBYRV4=; b=g2s1CDwYeUKSsFf51AeXZTtmaoN9C4VL/GLDNi2YxoJEHHm64z71k/YlwJ7Xw2+G9g jRxc27VwsInmy99MCVdvieVe7uMtwAFnMdP+4YjAey7hG6Ju9XXlR1yorkrHJW1V10hE YZyPxgHk6FxjvRFL7J9P+BeLiahGfuLHbSWPgtTlrLSnPSTJWb2m3qA92FY3+eBagapw sKo5GfhJPWMI1uFxPYG0EXuXe2me2P3d8YdXcL1T+y0eV2Iqv9dZHZ/gP9KIvz5WtV6B ZX2aM26bCnBrzlHWi1moZ67gTAmUOW4x45MDto6Bvb1OE/Bg0fzNcHaTxdYlKJ+ARJWA lmwQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=hhtnEx6dVeh1pIqAmosCNZhZcA/Z3fpbgOYNTfBYRV4=; b=Cv/uRlYYWgtl9UJFW+m14nFmYigsWqOhHb4qnIpY0lrU+vmmhqLq72aqs5B/8Cmj2T 2jRYel35jYroG5W5Dm4Yu+M8aii6CwV//pqNp7+pwhB7gL2nSSJSYj3HA67u/bkz/QNi aQOLp/+yfe3Q2H6eznhv+ZQeBcZzeJNA5/1c1Bk1MXCVHw5Kw2lZ4+dVkwo3BhGPtHRO ygds4Bqu8SjBx+B/iLuSdSP3uL3s3eEx6NpGzFd/sE6dN1ql75MogPj3SKP8xCjcwj1m RSnKUPwm+8AfSp6eeUcB3zr9llIK+EZ+LfriWckGEolfnewawcfZRXK7cOXuuMDQr1pK bn2Q== X-Gm-Message-State: AOAM530v4f7vLgafHsnhkMoxdWVILZY+zz93C46vXy6mqPJR0Ma41l6n bEEF1mucOlJX7oaRrEjohwE= X-Google-Smtp-Source: ABdhPJxBLRQw26sPOP45jGvpadgol3owKYDArwzGTR3fAUpm3H+PFbQX2BpsL1pSy+mq7KBNO7W0Lw== X-Received: by 2002:a17:90b:300d:: with SMTP id hg13mr4764487pjb.212.1594370588081; Fri, 10 Jul 2020 01:43:08 -0700 (PDT) Received: from localhost ([2409:10:2e40:5100:6e29:95ff:fe2d:8f34]) by smtp.gmail.com with ESMTPSA id j70sm5123354pfd.208.2020.07.10.01.43.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Jul 2020 01:43:07 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Fri, 10 Jul 2020 17:43:05 +0900 To: John Ogness Cc: Petr Mladek , 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: [PATCH v5 2/4] printk: add lockless ringbuffer Message-ID: <20200710084305.GA144760@jagdpanzerIV.localdomain> References: <20200709132344.760-1-john.ogness@linutronix.de> <20200709132344.760-3-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200709132344.760-3-john.ogness@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (20/07/09 15:29), John Ogness wrote: [..] > +/* > + * A data block: mapped directly to the beginning of the data block area > + * specified as a logical position within the data ring. > + * > + * @id: the ID of the associated descriptor > + * @data: the writer data > + * > + * Note that the size of a data block is only known by its associated > + * descriptor. > + */ > +struct prb_data_block { > + unsigned long id; > + char data[0]; > +}; A nit: I think someone will send "Replace zero-length arrays with flexible array member" soon enough: - char data[0]; + char data[]; [..] > +/* > + * Sanity checker for reserve size. The ringbuffer code assumes that a data > + * block does not exceed the maximum possible size that could fit within the > + * ringbuffer. This function provides that basic size check so that the > + * assumption is safe. > + * > + * Writers are also not allowed to write 0-sized (data-less) records. Such > + * records are used only internally by the ringbuffer. > + */ > +static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size) > +{ > + struct prb_data_block *db = NULL; > + > + /* > + * Writers are not allowed to write data-less records. Such records > + * are used only internally by the ringbuffer to denote records where > + * their data failed to allocate or have been lost. > + */ A nit: The same data-less records comment is some 5 lines earlier. But OK. > + if (size == 0) > + return false; [..] > +void prb_init(struct printk_ringbuffer *rb, > + char *text_buf, unsigned int textbits, > + char *dict_buf, unsigned int dictbits, > + struct prb_desc *descs, unsigned int descbits) > +{ > + memset(descs, 0, _DESCS_COUNT(descbits) * sizeof(descs[0])); > + > + rb->desc_ring.count_bits = descbits; > + rb->desc_ring.descs = descs; > + atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits)); > + atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits)); > + > + rb->text_data_ring.size_bits = textbits; > + rb->text_data_ring.data = text_buf; > + atomic_long_set(&rb->text_data_ring.head_lpos, BLK0_LPOS(textbits)); > + atomic_long_set(&rb->text_data_ring.tail_lpos, BLK0_LPOS(textbits)); > + > + rb->dict_data_ring.size_bits = dictbits; > + rb->dict_data_ring.data = dict_buf; > + atomic_long_set(&rb->dict_data_ring.head_lpos, BLK0_LPOS(dictbits)); > + atomic_long_set(&rb->dict_data_ring.tail_lpos, BLK0_LPOS(dictbits)); > + Just a side note: some people want !CONFIG_PRINTK builds. I wonder how many people will want !CONFIG_PRINTK_DICT. The core logbuf/dict logbuf split is really cool. -ss