Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752817AbaBXNYW (ORCPT ); Mon, 24 Feb 2014 08:24:22 -0500 Received: from lxorguk.ukuu.org.uk ([81.2.110.251]:39359 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752658AbaBXNYU (ORCPT ); Mon, 24 Feb 2014 08:24:20 -0500 Date: Mon, 24 Feb 2014 13:23:34 +0000 From: One Thousand Gnomes To: Thomas Gleixner Cc: Peter Hurley , Hal Murray , Stanislaw Gruszka , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-rt-users@vger.kernel.org, Greg Kroah-Hartman Subject: Re: locking changes in tty broke low latency feature Message-ID: <20140224132334.313f2527@alan.etchedpixels.co.uk> In-Reply-To: References: <20140219230623.736E8406062@ip-64-139-1-69.sjc.megapath.net> <53056E99.9070900@hurleysoftware.com> <53064672.3000807@hurleysoftware.com> Organization: Intel Corporation X-Mailer: Claws Mail 3.8.1 (GTK+ 2.24.20; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > This is a complete pointless test. Use a bog standard 8250 UART on the > PC and connect a microcontroller on the other end which serves you an > continous stream of data at 115200 Baud. > > There is no way you can keep up with that without the low latency > option neither on old and nor on new machines if you have enough other > stuff going on in the system. Sorry but having done this in the past the reverse is true. On ancient machines with crap uarts the low_latency case would routinely overrun while the non low_latency case did not. That was half of the point of deferred processing - it pushed tty processing out of the IRQ handler so bytes were not lost and a 486DX could cope with a 56Kbit modem. Alan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/