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 D6A28C433EF for ; Wed, 16 Mar 2022 15:27:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348548AbiCPP2r convert rfc822-to-8bit (ORCPT ); Wed, 16 Mar 2022 11:28:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36946 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229528AbiCPP2p (ORCPT ); Wed, 16 Mar 2022 11:28:45 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id D45A4673D5 for ; Wed, 16 Mar 2022 08:27:30 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-38-f6wgHKZ6OgqCN6WP2rtJ0g-1; Wed, 16 Mar 2022 15:27:27 +0000 X-MC-Unique: f6wgHKZ6OgqCN6WP2rtJ0g-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.32; Wed, 16 Mar 2022 15:27:26 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.033; Wed, 16 Mar 2022 15:27:26 +0000 From: David Laight To: 'Wander Lairson Costa' , Greg Kroah-Hartman , Jiri Slaby , Johan Hovold , "Maciej W. Rozycki" , Serge Semin , Lukas Wunner , =?iso-8859-1?Q?Pali_Roh=E1r?= , "open list:SERIAL DRIVERS" , open list CC: "rostedt@goodmis.org" , "senozhatsky@chromium.org" , "andre.goddard@gmail.com" , "sudipm.mukherjee@gmail.com" , "andy.shevchenko@gmail.com" , "jonathanh@nvidia.com" , "phil@raspberrypi.com" Subject: RE: [PATCH v4 1/5] serial/8250: Use fifo in 8250 console driver Thread-Topic: [PATCH v4 1/5] serial/8250: Use fifo in 8250 console driver Thread-Index: AQHYOUNg+UxO79+xmUuDTD6Kl8POG6zCIVEg Date: Wed, 16 Mar 2022 15:27:26 +0000 Message-ID: References: <20220316143646.13301-1-wander@redhat.com> <20220316143646.13301-2-wander@redhat.com> In-Reply-To: <20220316143646.13301-2-wander@redhat.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wander Lairson Costa > Sent: 16 March 2022 14:37 > > Note: I am using a small test app + driver located at [0] for the > problem description. serco is a driver whose write function dispatches > to the serial controller. sertest is a user-mode app that writes n bytes > to the serial console using the serco driver. > > While investigating a bug in the RHEL kernel, I noticed that the serial > console throughput is way below the configured speed of 115200 bps in > a HP Proliant DL380 Gen9. I was expecting something above 10KB/s, but > I got 2.5KB/s. > > $ time ./sertest -n 2500 /tmp/serco > > real 0m0.997s > user 0m0.000s > sys 0m0.997s > > With the help of the function tracer, I then noticed the serial > controller was taking around 410us seconds to dispatch one single byte: Did you verify the baud rate? Or is there some horrid serial redirection going on. It is even possible there is a bios smm interrupt chugging through on another cpu core. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)