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 06DAEC433F5 for ; Thu, 17 Mar 2022 12:27:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233555AbiCQM2u (ORCPT ); Thu, 17 Mar 2022 08:28:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230369AbiCQM2s (ORCPT ); Thu, 17 Mar 2022 08:28:48 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B36501EB80B for ; Thu, 17 Mar 2022 05:27:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647520051; 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=OrgWgBIoJfzLisqsnqNuO2T4Ox23yYSbOeMePAqRbx0=; b=U+GQlWssHEn87SJBB10dO8yE2DRojQCwuiLX+YBTkjehhVdVzLtkB0uY5Vwa5lGGVwQyUn ZEmdL3fhBw2OczSF3+F8fsZXTWb5OZKDrtSST3qqbEK7P7JCqgqjRSnVIsQzX5lYVCfiFK YfDnqRw4vcyt/z8gWD/ryEd+W/jt90k= Received: from mail-lj1-f197.google.com (mail-lj1-f197.google.com [209.85.208.197]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-1-NsMpcS1OM0m7EJhZR_it8A-1; Thu, 17 Mar 2022 08:27:23 -0400 X-MC-Unique: NsMpcS1OM0m7EJhZR_it8A-1 Received: by mail-lj1-f197.google.com with SMTP id 20-20020a2e0914000000b0024635d136ddso1999411ljj.22 for ; Thu, 17 Mar 2022 05:27:23 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=OrgWgBIoJfzLisqsnqNuO2T4Ox23yYSbOeMePAqRbx0=; b=hKcd/rk71pu/Y9Allb9iz0fQdmshQ0sHycBUV688UWAp9hM1nTJrNg9S8VX5ChMyI1 r632+SHNxztIwFViStlAo2JskCbK5Ruw3j03sI4r5FELm4eVa8K15gIwzO+AqXTOoD6v 6e6zS2g6Gl5c52xiZ6TTPhjbCwB2R2DFqJciSIRpGgmtci6faP4u04ZVkOwvFyQrYxm8 JqKcPROnSCy1Pvph1Zn9rwut8zNt1iAUZyNp+cQ3n9Pne/sh/safBmPD4wu+XouP2jSU l9JEdqvb0zz6c/SUgxM5Uwn5QTf/Q+LB7hMUlMgAbAsQUJm/7VErmZtRN49J8eO/1yx1 8gDQ== X-Gm-Message-State: AOAM533TBx2rpsDkn8UX6ta61iIt/mCpaXntdlQtn66MOQ+vOBNJtWbj FZMwVZCEhvX8q986O1gTOt0YaTrY2UlxOd8QGLKrsBSbcV1Yqpfi16ZnC/QJ7RcbndQOa4jRh4J ovMcXBPL6FjdIl7oYpOfhIomqZ/8FqT8HVUQ/GgYj X-Received: by 2002:a19:dc50:0:b0:448:816d:2dd8 with SMTP id f16-20020a19dc50000000b00448816d2dd8mr2648361lfj.1.1647520042121; Thu, 17 Mar 2022 05:27:22 -0700 (PDT) X-Google-Smtp-Source: ABdhPJz2dlOWq1WsEvaFd/fI5iXCgVuOFH/IMSoSaQ5HcG/HFbLEshYRc4GQrRKi3PVGw5rYMSPnEtv/ni99n4bLH0E= X-Received: by 2002:a19:dc50:0:b0:448:816d:2dd8 with SMTP id f16-20020a19dc50000000b00448816d2dd8mr2648335lfj.1.1647520041938; Thu, 17 Mar 2022 05:27:21 -0700 (PDT) MIME-Version: 1.0 References: <20220316143646.13301-1-wander@redhat.com> <20220316143646.13301-2-wander@redhat.com> In-Reply-To: From: Wander Costa Date: Thu, 17 Mar 2022 09:27:10 -0300 Message-ID: Subject: Re: [PATCH v4 1/5] serial/8250: Use fifo in 8250 console driver To: David Laight Cc: Wander Lairson Costa , Greg Kroah-Hartman , Jiri Slaby , Johan Hovold , "Maciej W. Rozycki" , Serge Semin , Lukas Wunner , =?UTF-8?Q?Pali_Roh=C3=A1r?= , "open list:SERIAL DRIVERS" , open list , "rostedt@goodmis.org" , "senozhatsky@chromium.org" , "andre.goddard@gmail.com" , "sudipm.mukherjee@gmail.com" , "andy.shevchenko@gmail.com" , "jonathanh@nvidia.com" , "phil@raspberrypi.com" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 16, 2022 at 12:27 PM David Laight wrote: > > 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? > Yes. > 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. > I would be surprised if that were the case because I see the problem even in low system activity. Someone in a previous patch-revision theorized this might be due to a bad serial controller emulator implemented in hardware (or something in this line of thought).