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Re: [Xen-devel] [PATCH v7 5/9] PCI: Add pci_iomap_wc() variants
- To: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
- From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
- Date: Fri, 26 Jun 2015 21:31:58 +0200
- Cc: linux-fbdev <linux-fbdev@xxxxxxxxxxxxxxx>, "Michael S. Tsirkin" <mst@xxxxxxxxxx>, "linux-pci@xxxxxxxxxxxxxxx" <linux-pci@xxxxxxxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, ville.syrjala@xxxxxxxxxxxxxxx, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Antonino Daplas <adaplas@xxxxxxxxx>, Tomi Valkeinen <tomi.valkeinen@xxxxxx>, Daniel Vetter <daniel.vetter@xxxxxxxx>, Dave Airlie <airlied@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Jean-Christophe Plagniol-Villard <plagnioj@xxxxxxxxxxxx>, Casey Leedom <leedom@xxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Suresh Siddha <sbsiddha@xxxxxxxxx>, Stefan Bader <stefan.bader@xxxxxxxxxxxxx>, Bjorn Helgaas <bhelgaas@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Toshi Kani <toshi.kani@xxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxxxxxx>, David Vrabel <david.vrabel@xxxxxxxxxx>, "venkatesh.pallipadi@xxxxxxxxx" <venkatesh.pallipadi@xxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Fri, 26 Jun 2015 19:32:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On Fri, Jun 26, 2015 at 08:51:58AM +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2015-06-25 at 21:40 +0000, Casey Leedom wrote:
> > Hhmmm, so what do PowerPC Drivers do when they want to take
> > advantage of Write Combining? Do their own Endian Swizzling
> > with the __raw_*() APIs?
>
> 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?
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.
Luis
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