Groups > linux.kernel > #1312034

Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables

Path	csiph.com!goblin2!goblin1!goblin.stu.neva.ru!news.mixmin.net!aioe.org!bofh.it!news.nic.it!robomod
From	Jean Delvare <jdelvare@suse.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables
Date	Tue, 19 Jan 2016 10:20:02 +0100
Message-ID	<qSACe-5IF-21@gated-at.bofh.it> (permalink)
References	<qMSiu-6Jn-11@gated-at.bofh.it> <qPSFk-8fi-7@gated-at.bofh.it> <qQ87p-28L-35@gated-at.bofh.it> <qQC5s-67v-5@gated-at.bofh.it> <qRcBY-6DV-15@gated-at.bofh.it> <qRfqa-cf-13@gated-at.bofh.it> <qRgPh-ZC-9@gated-at.bofh.it> <qRiR5-2yH-25@gated-at.bofh.it>
Organization	SUSE Linux
X-Mailer	Claws Mail 3.10.1 (GTK+ 2.24.23; x86_64-suse-linux-gnu)
MIME-Version	1.0
Content-Type	text/plain; charset=US-ASCII
Content-Transfer-Encoding	7bit
Sender	robomod@news.nic.it
List-ID	<linux-kernel.vger.kernel.org>
X-Mailing-List	linux-kernel@vger.kernel.org
Approved	robomod@news.nic.it
Lines	32
X-Original-Cc	Pali Rohár <pali.rohar@gmail.com>, platform-driver-x86@vger.kernel.org, linux-kernel <linux-kernel@vger.kernel.org>
X-Original-Date	Tue, 19 Jan 2016 10:12:01 +0100
X-Original-Message-ID	<20160119101201.49c4d4c5@endymion.delvare>
X-Original-References	<119170b95d373bc943eb4f16818239bac9fa6c59.1451832667.git.luto@kernel.org> <CALCETrVZ23t8u34VtgC+VVQC4PQ0JAw2u27+W_MQiwS=BgMAXQ@mail.gmail.com> <20160112142538.GB11560@pali> <CALCETrWUJ+5DowyLFDp7N_iNLsday4uKX3iO3NMC8Pfqma=O7w@mail.gmail.com> <20160115142719.36eea015@endymion.delvare> <CALCETrWXVxYLP0yTg4hS7JFjccjskvAF79ec6iSZsKJbLYi9GQ@mail.gmail.com> <1452880405.4941.0.camel@chaos.site> <CALCETrWsm1OVuZQNeU-UkcdNg1rt6Wu9CKY=xc_0M9kKzedYYg@mail.gmail.com>
X-Original-Sender	linux-kernel-owner@vger.kernel.org
Xref	csiph.com linux.kernel:1312034

Show key headers only | View raw

Hi Andy,

On Fri, 15 Jan 2016 12:00:02 -0800, Andy Lutomirski wrote:
> UC means uncached.  ioremap, on x86, asks for an uncached mapping, so
> every memory access (load or store) hits main memory individually.
> Assuming that the spec says that whatever physical memory the DMI
> tables live in is permitted to be used with cached accesses, asking
> for the CPU cache to be permitted on those accesses will make them a
> whole lot faster.
> 
> If that isn't safe, you could also just copy each table out of the
> ioremap space into normal RAM as needed using MOVNTDQA.  I forget what
> the helper for that is called, but it basically does a fast streaming
> IO read and then writes to normal RAM, memcpy style.  Most modern CPUs
> support it.

I have no idea what is allowed and what isn't, sorry. You would have to
check the SMBIOS specification but also the UEFI specification.

I have to admit I never understood why dmi_alloc is arch-specific nor
why dmi_remap is needed in the first place (and even less why
dmi_early_remap is different.) So I'm not going to mess up with that
code.

I have no idea how costly dmi_remap() is, but certainly it is being
called more and more as we can see dmi_walk() gaining in popularity. So
if anyone is worried about the performance, I'll be happy to review and
test patches.

-- 
Jean Delvare
SUSE L3 Support

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-15 14:30 +0100
  Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@amacapital.net> - 2016-01-15 17:30 +0100
    Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-15 19:00 +0100
      Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Andy Lutomirski <luto@amacapital.net> - 2016-01-15 21:10 +0100
        Re: [PATCH] dell-wmi: Stop storing pointers to DMI tables Jean Delvare <jdelvare@suse.de> - 2016-01-19 10:20 +0100

csiph-web