Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752671AbdGRXQU (ORCPT ); Tue, 18 Jul 2017 19:16:20 -0400 Received: from mail-ua0-f179.google.com ([209.85.217.179]:33495 "EHLO mail-ua0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751513AbdGRXQS (ORCPT ); Tue, 18 Jul 2017 19:16:18 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170718060909.5280-1-airlied@redhat.com> <20170718143404.omgxrujngj2rhiya@redhat.com> From: Dave Airlie Date: Wed, 19 Jul 2017 09:16:17 +1000 Message-ID: Subject: Re: [PATCH] efifb: allow user to disable write combined mapping. To: Linus Torvalds Cc: Peter Jones , "the arch/x86 maintainers" , Dave Airlie , Bartlomiej Zolnierkiewicz , "linux-fbdev@vger.kernel.org" , Linux Kernel Mailing List , Andrew Lutomirski , Peter Anvin Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1748 Lines: 39 On 19 July 2017 at 08:22, Linus Torvalds wrote: > On Tue, Jul 18, 2017 at 2:21 PM, Dave Airlie wrote: >> >> Oh and just FYI, the machine I've tested this on has an mgag200 server >> graphics card backing the framebuffer, but with just efifb loaded. > > Yeah, it looks like it needs special hardware - and particularly the > kind of garbage hardware that people only have on servers. > > Why do server people continually do absolute sh*t hardware? It's crap, > crap, crap across the board outside the CPU. Nasty and bad hacky stuff > that nobody else would touch with a ten-foot pole, and the "serious > enterprise" people lap it up like it was ambrosia. > > It's not just "graphics is bad anyway since we don't care". It's all > the things they ostensibly _do_ care about too, like the disk and the > fabric infrastructure. Buggy nasty crud. I've tried to reproduce now on: Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz using some address space from 02:00.0 3D controller: NVIDIA Corporation GM108M [GeForce 940MX] (rev a2) And I don't see the issue. I'll try and track down some more efi compatible mga or other wierd server chips stuff if I can. > Anyway, rant over. I wonder if we could show this without special > hardware by just mapping some region that doesn't even have hardware > in it as WC. Do we even expose the PAT settings to user space, though, > or do we always have to have some fake module to create the PAT stuff? I do wonder wtf the hw could be doing that would cause this, but I've no idea how to tell what difference a write combined PCI transaction would have on the bus side of things, and what the device could generate that would cause such a horrible slowdown. Dave.