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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 77233C4167B for ; Sun, 10 Dec 2023 14:17:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232531AbjLJORl (ORCPT ); Sun, 10 Dec 2023 09:17:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60754 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229584AbjLJORj (ORCPT ); Sun, 10 Dec 2023 09:17:39 -0500 Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9209F4; Sun, 10 Dec 2023 06:17:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1702217865; bh=95FOqqEVlvMpVu60xKcTVHAxKd+ad692k9vCay/7OIc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=SmGi6NmMr8M8UM9SD93vDg7+H16lkzxZdbVZdUOSatOmwq0RRnP7D8ItJLGmLth6g MuRFqYbO0B82vEExpJ8fjRpe/ahu15CUQfWpiZotn1/7fDIuMY0J+76xyM45/VOx/r VcD9qhLu1WR9H1yb89kYapLAQ5zXCgpevNlfFXL5t8A3wIiNvIhY1tcc96gPnH4Eoi TBKnN5iSi1etbYHoDHF3WQdCCFW9lvHbjvH6CfxrZbBWQfDlxb6pLDucIV1bTM8dKm 617ArDJcUam1f3728aghyIvZQkMVkT+qGlKP96QLDbr6le4gJ5gPgZmXld0Pjxfqah WShryYQuXOS7g== Received: from [IPV6:2606:6d00:100:4000:cacb:9855:de1f:ded2] (unknown [IPv6:2606:6d00:100:4000:cacb:9855:de1f:ded2]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4Sp6Qw6jlVzFr3; Sun, 10 Dec 2023 09:17:44 -0500 (EST) Message-ID: <76797ddd-bb87-4af9-9703-1ec00a0d318c@efficios.com> Date: Sun, 10 Dec 2023 09:17:44 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/14] ring-buffer/tracing: Allow ring buffer to have bigger sub buffers Content-Language: en-US To: Steven Rostedt , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Andrew Morton , Tzvetomir Stoyanov , Vincent Donnefort , Kent Overstreet References: <20231210035404.053677508@goodmis.org> From: Mathieu Desnoyers In-Reply-To: <20231210035404.053677508@goodmis.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023-12-09 22:54, Steven Rostedt wrote: [...] > > Basically, events to the tracing subsystem are limited to just under a > PAGE_SIZE, as the ring buffer is split into "sub buffers" of one page > size, and an event can not be bigger than a sub buffer. This allows users > to change the size of a sub buffer by the order: > > echo 3 > /sys/kernel/tracing/buffer_subbuf_order > > Will make each sub buffer a size of 8 pages, allowing events to be almost > as big as 8 pages in size (sub buffers do have meta data on them as > well, keeping an event from reaching the same size as a sub buffer). Specifying the "order" of subbuffer size as a power of two of number of pages is a poor UX choice for a user-facing ABI. I would recommend allowing the user to specify the size in bytes, and internally bump to size to the next power of 2, with a minimum of PAGE_SIZE. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com