From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 06D83C28CF6 for ; Fri, 3 Aug 2018 12:04:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AD9C02175E for ; Fri, 3 Aug 2018 12:04:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AD9C02175E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727595AbeHCOAh (ORCPT ); Fri, 3 Aug 2018 10:00:37 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:40090 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727291AbeHCOAh (ORCPT ); Fri, 3 Aug 2018 10:00:37 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1D001819701E; Fri, 3 Aug 2018 12:04:35 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A8CB81CBBF; Fri, 3 Aug 2018 12:04:34 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id w73C4Ygd014850; Fri, 3 Aug 2018 08:04:34 -0400 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id w73C4WfT014841; Fri, 3 Aug 2018 08:04:33 -0400 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Fri, 3 Aug 2018 08:04:32 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: David Laight cc: "'Ard Biesheuvel'" , Ramana Radhakrishnan , Florian Weimer , Thomas Petazzoni , GNU C Library , Andrew Pinski , Catalin Marinas , Will Deacon , Russell King , LKML , linux-arm-kernel Subject: RE: framebuffer corruption due to overlapping stp instructions on arm64 In-Reply-To: Message-ID: References: <9acdacdb-3bd5-b71a-3003-e48132ee1371@redhat.com> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 03 Aug 2018 12:04:35 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 03 Aug 2018 12:04:35 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'mpatocka@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 3 Aug 2018, David Laight wrote: > From: Ard Biesheuvel > > Sent: 03 August 2018 10:30 > ... > > The discussion about whether memcpy() should rely on unaligned > > accesses, and whether you should use it on device memory is orthogonal > > to that, and not the heart of the matter IMO > > Even on x86 using memcpy() on PCIe memory (maybe mmap()ed into userspace) > isn't a good idea. > In the kernel memcpy_to/fromio() ought to be a better choice but that > is just an alternate name for memcpy(). > > The problem on x86 is that memcpy() is likely to be implemented as > 'rep movsb' on modern cpu - relying on the cpu hardware to perform > cache-line sized transfers (etc). > Unfortunately on uncached locations it has to revert to byte copies. > So PCIe transfers (especially reads) are very slow. > > The transfers need to use the largest size register available. > > David On x86, the framebuffer is mapped as write-combining memory type, so "rep movsb" could merge the byte writes to larger chunks. I don't have a cpu with the ERMS feature - could anyone try it if rep movsb works worse or better than explicit writes to the framebuffer? Mikulas