From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932755AbaICPKu (ORCPT ); Wed, 3 Sep 2014 11:10:50 -0400 Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:49734 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932641AbaICPKr (ORCPT ); Wed, 3 Sep 2014 11:10:47 -0400 Message-ID: <54072F75.70107@hurleysoftware.com> Date: Wed, 03 Sep 2014 11:10:45 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 MIME-Version: 1.0 To: One Thousand Gnomes CC: Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 21/26] tty: Convert tty_struct bitfield to bools References: <1409693975-1028-1-git-send-email-peter@hurleysoftware.com> <1409693975-1028-22-git-send-email-peter@hurleysoftware.com> <20140903115852.5a720754@alan.etchedpixels.co.uk> <54070643.9080903@hurleysoftware.com> <20140903131919.0d970b6f@alan.etchedpixels.co.uk> In-Reply-To: <20140903131919.0d970b6f@alan.etchedpixels.co.uk> Content-Type: text/plain; charset=utf-8 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 09/03/2014 08:19 AM, One Thousand Gnomes wrote: >> Ahh. Thanks for the insight, Alan. >> >> But set_bit() et. al. will generate an incredible amount of churn; >> what if I split the fields up to prevent false-sharing? > > Do you feel lucky ;-) Hahaha :) > I'd rather set_bit and friends were used. They exist largely for this > kind of reason and they also have atomic test/set methods which may in > the longer term be very useful. > > Yes it is churn can't argue with that. Yuck. There should be a better way. IXANY mode is suddenly going to have a ton of unnecessary bus locks on x86. Note the ctrl_status field is a byte as well, which can't be RMW'ed by the bit-locked primitives, and definitely should not be aggregated with any adjacent field. Regards, Peter Hurley