Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966095AbbBCPyg (ORCPT ); Tue, 3 Feb 2015 10:54:36 -0500 Received: from 251.110.2.81.in-addr.arpa ([81.2.110.251]:43174 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756141AbbBCPyc (ORCPT ); Tue, 3 Feb 2015 10:54:32 -0500 Date: Tue, 3 Feb 2015 15:54:02 +0000 From: One Thousand Gnomes To: Linus Torvalds Cc: Dave Airlie , Linux Kernel Mailing List , dri-devel@lists.sf.net, Greg Kroah-Hartman , Tomi Valkeinen Subject: Re: [PATCH] vt_buffer: drop console buffer copying optimisations Message-ID: <20150203155402.4c31c36b@lxorguk.ukuu.org.uk> In-Reply-To: References: <1422504685-7864-1-git-send-email-airlied@redhat.com> Organization: Intel Corporation X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-redhat-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 Content-Length: 1749 Lines: 43 On Thu, 29 Jan 2015 15:40:33 -0800 Linus Torvalds wrote: > On Wed, Jan 28, 2015 at 8:11 PM, Dave Airlie wrote: > > > > Linus, this came up a while back I finally got some confirmation > > that it fixes those servers. > > I'm certainly ok with this. which way should it go in? The users are: > > - drivers/tty/vt/vt.c (Greg KH, "tty layer") > > - drivers/video/console/* (fbcon people: Tomi Valkeinen and friends) > > and it might make sense to have *some* indication of how much worse > this makes fbcon performance in particular.. For devices that have no hardware scrolling it used to be double digit percentages difference between 32 and 64bit when reading from the fb because the reads are not posted and the latency killed you. Writes - not so big a deal - but the bridge should combine them anyway. I imagine 16bit read would be unprintably bad. Is it reads or writes that kill the card ? Also note that switching to lots of small writes may break the 3Dfx driver for the early 3Dfx PCI cards - they are really quite touchy about how they are fed. Unfortunately fbcon still matters for dumb EFI framebuffer fallbacks. vgacon it doesn't matter (if it was too slow you could make vgacon as fast as you want by only updating the off screen characters once per vertical blank). fbcon that is a bit harder as you are allowed to scribble on the display as well. You can't even check open/mmapped as you can open, scribble and close. 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/