Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 22 Mar 2001 17:46:29 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 22 Mar 2001 17:46:20 -0500 Received: from pcp001515pcs.wireless.meeting.ietf.org ([135.222.67.247]:64775 "EHLO think") by vger.kernel.org with ESMTP id ; Thu, 22 Mar 2001 17:46:02 -0500 Date: Thu, 22 Mar 2001 16:44:57 -0600 From: Theodore Tso To: Geir Thomassen Cc: Theodore Tso , linux-kernel@vger.kernel.org Subject: Re: Serial port latency Message-ID: <20010322164457.A4886@think> Mail-Followup-To: Theodore Tso , Geir Thomassen , linux-kernel@vger.kernel.org In-Reply-To: <3ABA42A8.A806D0E7@powertech.no> <20010322140852.A4110@think> <3ABA6167.309E6DB2@powertech.no> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.3.15i In-Reply-To: <3ABA6167.309E6DB2@powertech.no>; from geirt@powertech.no on Thu, Mar 22, 2001 at 09:32:39PM +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 22, 2001 at 09:32:39PM +0100, Geir Thomassen wrote: > > The serial port chip is 16550A, which has a built in fifo. Can this be > the source of my problems ? Well, if you set the uart to be 16450 using setserial, this will cause Linux to avoid enabling the FIFO. That will cause the loop to save the 4 character times (which at 9600 bps is 4ms). If your original protocol is writing six characters, and then reads 2 characters in a tight loop, that means a total cycle takes 8ms, and disabling the FIFO will have significant savings assuming that all other causes of latencies have been removed. (The FIFO delay can cause a slowdown by 50%). - Ted - 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/