linux-kernel - Re: [PATCH v7 5/9] PCI: Add pci_iomap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 27 Jun 2015 08:04:18 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	Casey Leedom <leedom@...lsio.com>, Arnd Bergmann <arnd@...db.de>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Toshi Kani <toshi.kani@...com>,
	Andy Lutomirski <luto@...capital.net>,
	Juergen Gross <jgross@...e.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	linux-fbdev <linux-fbdev@...r.kernel.org>,
	Suresh Siddha <sbsiddha@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	Antonino Daplas <adaplas@...il.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"venkatesh.pallipadi@...el.com" <venkatesh.pallipadi@...el.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	ville.syrjala@...ux.intel.com,
	David Vrabel <david.vrabel@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	Roger Pau Monné <roger.pau@...rix.com>
Subject: Re: [PATCH v7 5/9] PCI: Add pci_iomap_wc() variants

On Fri, 2015-06-26 at 21:31 +0200, Luis R. Rodriguez wrote:
> > Yeah either, we need to fix our relaxed implementation (patch
> > welcome :-)
> 
> Yikes, so although powerpc has useful heuristics to automatically
> enable WC the default write ops have been nullifying its effects?

The heuristic is for userspace mapping which don't use the kernel
accessors. To cut a long story short, this was all done back in the day
to speed up X.org which doesn't use fancy accessors with barriers to
access the framebuffer (neither does the kernel fbdev layer).

> Shouldn't this have been blatantly obvious in performance benchmarks
> and expectations? 

> If not a change should give considerable performance
> gains... If the WC was nullified on powerpc then the experience and
> value of the heuristics have less value and even if they are going
> to be only considered for userspace mmap() it should be taken with
> a bit grain of salt it seems.

It wasn't nullified for the main user at the time, the fb. And I
mentioned an IB adapter or two for which the code had been hand tuned.

Cheers,
Ben.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/