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 E386EC433EF for ; Fri, 1 Apr 2022 16:33:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347569AbiDAQfL (ORCPT ); Fri, 1 Apr 2022 12:35:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41168 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348318AbiDAQew (ORCPT ); Fri, 1 Apr 2022 12:34:52 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0D3BC22EE49; Fri, 1 Apr 2022 09:07:24 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 603C2CE2414; Fri, 1 Apr 2022 16:07:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F380DC2BBE4; Fri, 1 Apr 2022 16:07:06 +0000 (UTC) Date: Fri, 1 Apr 2022 12:07:05 -0400 From: Steven Rostedt To: Jiri Slaby Cc: Wander Lairson Costa , Greg Kroah-Hartman , Johan Hovold , "Maciej W. Rozycki" , Andy Shevchenko , Lukas Wunner , Pali =?UTF-8?B?Um9ow6Fy?= , "open list:SERIAL DRIVERS" , open list , senozhatsky@chromium.org, andre.goddard@gmail.com, sudipm.mukherjee@gmail.com, andy.shevchenko@gmail.com, David.Laight@aculab.com, jonathanh@nvidia.com, phil@raspberrypi.com Subject: Re: [PATCH v5 1/1] serial/8250: Use fifo in 8250 console driver Message-ID: <20220401120705.533896e5@gandalf.local.home> In-Reply-To: <4767809d-5818-ad40-a0e7-b3af40aa071e@kernel.org> References: <20220331190257.101781-1-wander@redhat.com> <20220331190257.101781-2-wander@redhat.com> <4767809d-5818-ad40-a0e7-b3af40aa071e@kernel.org> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 1 Apr 2022 06:35:58 +0200 Jiri Slaby wrote: > > With the help of the function tracer, I then noticed the serial > > controller was taking around 410us seconds to dispatch one single byte: > > > > $ trace-cmd record -p function_graph -g serial8250_console_write \ > > ./sertest -n 1 /tmp/serco > > > > $ trace-cmd report > > Note, the function graph tracer can add a noticeable amount of overhead to these timings. If you want a more accurate time for a function, just trace that one function: trace-cmd record -p function_graph -l serial8250_console_write ... As that will only trace the serial8250_console_write() function (think of -l as "limit"), and the overhead of function graph for tracing a single function becomes negligible, and then you can see the true time of that function. -- Steve