Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752898AbaBTWGP (ORCPT ); Thu, 20 Feb 2014 17:06:15 -0500 Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:57725 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751350AbaBTWGN (ORCPT ); Thu, 20 Feb 2014 17:06:13 -0500 Message-ID: <53067C50.9010708@hurleysoftware.com> Date: Thu, 20 Feb 2014 17:06:08 -0500 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Grant Edwards CC: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-rt-users@vger.kernel.org, Hal Murray , One Thousand Gnomes , Stanislaw Gruszka Subject: Re: locking changes in tty broke low latency feature References: <20140219230623.736E8406062@ip-64-139-1-69.sjc.megapath.net> <53056E99.9070900@hurleysoftware.com> <53064672.3000807@hurleysoftware.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated-User: 990527 peter@hurleysoftware.com X-MT-ID: 8FA290C2A27252AACF65DBC4A42F3CE3735FB2A4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/20/2014 02:33 PM, Grant Edwards wrote: > On 2014-02-20, Peter Hurley wrote: >> Sender completes 2000 loops in 160ms total run time; >> that's 80us average per complete round-trip. > > If I understand correctly, that 80us _includes_ the actual time for > the bits on the wire (which means the actual "baud rate" involved is > high enough that it's negligible). Yes, 80us includes the transmit time. >> I think this shows that low_latency is unnecessary and should >> just be removed/ignored by the tty core. > > If that's the sort of latency that you get for typical kernel > configurations for typical distros, then I agree that the low_latency > flag is not needed by the tty later. Stock ubuntu kernel config but preempt and 250hz (and debugging stuff). > However, it might still be useful for the lower-level tty or > serial-core driver to control CPU usage vs. latency trade-offs (for > exaple, one of my drivers uses it to decide where to set the rx FIFO > threshold). Sure, it could be left for driver consumption. Regards, Peter Hurley -- 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/