From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Thomas Hellstrom <thellstrom@vmware.com>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
Russell King - ARM Linux <linux@arm.linux.org.uk>,
Arnd Bergmann <arnd@arndb.de>,
linux-kernel@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
Jerome Glisse <j.glisse@gmail.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1
Date: Sat, 30 Apr 2011 08:50:56 +1000 [thread overview]
Message-ID: <1304117456.2513.265.camel@pasglop> (raw)
In-Reply-To: <4DBA990F.6040203@vmware.com>
On Fri, 2011-04-29 at 12:55 +0200, Thomas Hellstrom wrote:
> On 04/29/2011 09:35 AM, Benjamin Herrenschmidt wrote:
> >
> > We have problems with AGP and macs, we chose to mostly ignore them and
> > things have been working so-so ... with the old DRM. With DRI2 being
> > much more aggressive at mapping/unmapping things, things became a lot
> > less stable and it could be in part related to that. IE. Aliases are
> > similarily forbidden but we create them anyways.
> >
> Do you have any idea how other OS's solve this AGP issue on Macs?
> Using a fixed pool of write-combined pages?
Write-combine is a different business, it's a matter of not mapping with
the G bit, but no, the way MacOS works I think is that they don't
actually use large pages at all, and I don't even think they have a
linear mapping of all memory. On the other hand they are slow :-)
> >> c) If neither of the above applies, we might be able to either use
> >> explicit cache flushes (which will require a TTM cache sync API), or
> >> require the device to use snooping mode. The architecture may also
> >> perhaps have a pool of write-combined pages that we can use. This should
> >> be indicated by defines in the api header.
> >>
> > Right. We should still shoot HW designers who give up coherency for the
> > sake of 3D benchmarks. It's insanely stupid.
> >
>
> I agree. From a driver writer's perspective having the GPU always
> snooping the system pages would be a dream. On the GPUs that do support
> snooping that I have looked at, its internal MMU usually support both
> modes, but the snooping mode is way slower (we're talking 50-70% or so
> slower texturing operations), and often buggy causing crashes or scanout
> timing issues since system designers apparently don't really count on it
> being used. I've found it usable for device-to-system memory blits.
>
> In addition memcpy to device is usually way faster if the destination is
> write-combined. Probably due to cache thrashing effects.
Possibly. It's a matter of the HW folks actually spending some time to
make it work properly. It can be done :-) It's just that they don't
bother. Look at the perfs one can get out of fully coherent PCIe
nowadays, largely enough for a simple scanout :-)
Cheers,
Ben.
> /Thomas
>
> > Cheers,
> > Ben.
> >
> >
> >> /Thomas
> >>
> >>
> >>
> >>
> >>
> >>> _______________________________________________
> >>> Linaro-mm-sig mailing list
> >>> Linaro-mm-sig@lists.linaro.org
> >>> http://lists.linaro.org/mailman/listinfo/linaro-mm-sig
> >>>
> >>>
> >
> >
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: benh@kernel.crashing.org (Benjamin Herrenschmidt)
To: linux-arm-kernel@lists.infradead.org
Subject: [Linaro-mm-sig] [RFC] ARM DMA mapping TODO, v1
Date: Sat, 30 Apr 2011 08:50:56 +1000 [thread overview]
Message-ID: <1304117456.2513.265.camel@pasglop> (raw)
In-Reply-To: <4DBA990F.6040203@vmware.com>
On Fri, 2011-04-29 at 12:55 +0200, Thomas Hellstrom wrote:
> On 04/29/2011 09:35 AM, Benjamin Herrenschmidt wrote:
> >
> > We have problems with AGP and macs, we chose to mostly ignore them and
> > things have been working so-so ... with the old DRM. With DRI2 being
> > much more aggressive at mapping/unmapping things, things became a lot
> > less stable and it could be in part related to that. IE. Aliases are
> > similarily forbidden but we create them anyways.
> >
> Do you have any idea how other OS's solve this AGP issue on Macs?
> Using a fixed pool of write-combined pages?
Write-combine is a different business, it's a matter of not mapping with
the G bit, but no, the way MacOS works I think is that they don't
actually use large pages at all, and I don't even think they have a
linear mapping of all memory. On the other hand they are slow :-)
> >> c) If neither of the above applies, we might be able to either use
> >> explicit cache flushes (which will require a TTM cache sync API), or
> >> require the device to use snooping mode. The architecture may also
> >> perhaps have a pool of write-combined pages that we can use. This should
> >> be indicated by defines in the api header.
> >>
> > Right. We should still shoot HW designers who give up coherency for the
> > sake of 3D benchmarks. It's insanely stupid.
> >
>
> I agree. From a driver writer's perspective having the GPU always
> snooping the system pages would be a dream. On the GPUs that do support
> snooping that I have looked at, its internal MMU usually support both
> modes, but the snooping mode is way slower (we're talking 50-70% or so
> slower texturing operations), and often buggy causing crashes or scanout
> timing issues since system designers apparently don't really count on it
> being used. I've found it usable for device-to-system memory blits.
>
> In addition memcpy to device is usually way faster if the destination is
> write-combined. Probably due to cache thrashing effects.
Possibly. It's a matter of the HW folks actually spending some time to
make it work properly. It can be done :-) It's just that they don't
bother. Look at the perfs one can get out of fully coherent PCIe
nowadays, largely enough for a simple scanout :-)
Cheers,
Ben.
> /Thomas
>
> > Cheers,
> > Ben.
> >
> >
> >> /Thomas
> >>
> >>
> >>
> >>
> >>
> >>> _______________________________________________
> >>> Linaro-mm-sig mailing list
> >>> Linaro-mm-sig at lists.linaro.org
> >>> http://lists.linaro.org/mailman/listinfo/linaro-mm-sig
> >>>
> >>>
> >
> >
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2011-04-29 22:51 UTC|newest]
Thread overview: 198+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-21 19:29 [RFC] ARM DMA mapping TODO, v1 Arnd Bergmann
2011-04-21 19:29 ` Arnd Bergmann
2011-04-21 20:09 ` [Linaro-mm-sig] " Jesse Barnes
2011-04-21 20:09 ` Jesse Barnes
2011-04-21 21:52 ` Zach Pfeffer
2011-04-21 21:52 ` Zach Pfeffer
2011-04-22 0:34 ` KyongHo Cho
2011-04-22 0:34 ` KyongHo Cho
2011-04-26 14:29 ` Arnd Bergmann
2011-04-26 14:29 ` Arnd Bergmann
2011-04-26 14:28 ` Arnd Bergmann
2011-04-26 14:28 ` Arnd Bergmann
2011-04-26 14:26 ` Arnd Bergmann
2011-04-26 14:26 ` Arnd Bergmann
2011-04-26 15:39 ` Jesse Barnes
2011-04-26 15:39 ` Jesse Barnes
2011-04-27 7:35 ` Russell King - ARM Linux
2011-04-27 7:35 ` Russell King - ARM Linux
2011-04-27 8:56 ` Arnd Bergmann
2011-04-27 8:56 ` Arnd Bergmann
2011-04-27 9:09 ` Russell King - ARM Linux
2011-04-27 9:09 ` Russell King - ARM Linux
2011-04-27 11:02 ` Arnd Bergmann
2011-04-27 11:02 ` Arnd Bergmann
2011-04-27 16:16 ` [Linaro-mm-sig] " Alex Deucher
2011-04-27 16:16 ` Alex Deucher
2011-04-27 17:44 ` Anca Emanuel
2011-04-27 17:44 ` Anca Emanuel
2011-04-27 20:27 ` Russell King - ARM Linux
2011-04-27 20:27 ` Russell King - ARM Linux
2011-04-27 20:16 ` Russell King - ARM Linux
2011-04-27 20:16 ` Russell King - ARM Linux
2011-04-27 20:21 ` Arnd Bergmann
2011-04-27 20:21 ` Arnd Bergmann
2011-04-27 20:26 ` Russell King - ARM Linux
2011-04-27 20:26 ` Russell King - ARM Linux
2011-04-27 20:48 ` Arnd Bergmann
2011-04-27 20:48 ` Arnd Bergmann
2011-04-27 21:41 ` Benjamin Herrenschmidt
2011-04-27 21:41 ` Benjamin Herrenschmidt
2011-04-28 9:30 ` Russell King - ARM Linux
2011-04-28 9:30 ` Russell King - ARM Linux
2011-04-28 21:07 ` Benjamin Herrenschmidt
2011-04-28 21:07 ` Benjamin Herrenschmidt
2011-04-29 11:26 ` Arnd Bergmann
2011-04-29 11:26 ` Arnd Bergmann
2011-04-29 11:47 ` Benjamin Herrenschmidt
2011-04-29 11:47 ` Benjamin Herrenschmidt
2011-04-29 11:56 ` Alan Cox
2011-04-29 11:56 ` Alan Cox
2011-04-29 22:51 ` Benjamin Herrenschmidt
2011-04-29 22:51 ` Benjamin Herrenschmidt
2011-04-29 12:06 ` [Linaro-mm-sig] " Thomas Hellstrom
2011-04-29 12:06 ` Thomas Hellstrom
2011-04-29 13:34 ` Jerome Glisse
2011-04-29 13:34 ` Jerome Glisse
2011-04-29 22:55 ` Benjamin Herrenschmidt
2011-04-29 22:55 ` Benjamin Herrenschmidt
2011-04-29 22:53 ` Benjamin Herrenschmidt
2011-04-29 22:53 ` Benjamin Herrenschmidt
2011-04-27 10:51 ` Marek Szyprowski
2011-04-27 10:51 ` Marek Szyprowski
2011-04-27 21:37 ` Benjamin Herrenschmidt
2011-04-27 21:37 ` Benjamin Herrenschmidt
2011-04-28 6:40 ` [Linaro-mm-sig] " Arnd Bergmann
2011-04-28 6:40 ` Arnd Bergmann
2011-04-28 6:46 ` FUJITA Tomonori
2011-04-28 6:46 ` FUJITA Tomonori
2011-04-28 9:37 ` Russell King - ARM Linux
2011-04-28 9:37 ` Russell King - ARM Linux
2011-04-28 10:32 ` [Linaro-mm-sig] " Marek Szyprowski
2011-04-28 10:32 ` Marek Szyprowski
2011-04-28 10:51 ` Russell King - ARM Linux
2011-04-28 10:51 ` Russell King - ARM Linux
2011-04-28 12:28 ` Arnd Bergmann
2011-04-28 12:28 ` Arnd Bergmann
2011-04-28 13:15 ` Russell King - ARM Linux
2011-04-28 13:15 ` Russell King - ARM Linux
2011-04-28 14:29 ` Arnd Bergmann
2011-04-28 14:29 ` Arnd Bergmann
2011-04-28 14:34 ` Russell King - ARM Linux
2011-04-28 14:34 ` Russell King - ARM Linux
2011-04-28 14:39 ` Arnd Bergmann
2011-04-28 14:39 ` Arnd Bergmann
2011-04-28 14:58 ` Russell King - ARM Linux
2011-04-28 14:58 ` Russell King - ARM Linux
2011-04-28 19:37 ` Jerome Glisse
2011-04-28 19:37 ` Jerome Glisse
2011-04-29 0:29 ` Benjamin Herrenschmidt
2011-04-29 0:29 ` Benjamin Herrenschmidt
2011-04-29 5:50 ` Thomas Hellstrom
2011-04-29 5:50 ` Thomas Hellstrom
2011-04-29 7:35 ` Benjamin Herrenschmidt
2011-04-29 7:35 ` Benjamin Herrenschmidt
2011-04-29 10:55 ` Thomas Hellstrom
2011-04-29 10:55 ` Thomas Hellstrom
2011-04-29 22:50 ` Benjamin Herrenschmidt [this message]
2011-04-29 22:50 ` Benjamin Herrenschmidt
2011-04-29 16:27 ` Jesse Barnes
2011-04-29 16:27 ` Jesse Barnes
2011-04-29 22:46 ` Benjamin Herrenschmidt
2011-04-29 22:46 ` Benjamin Herrenschmidt
2011-04-30 2:45 ` Jesse Barnes
2011-04-30 2:45 ` Jesse Barnes
2011-04-29 7:59 ` Russell King - ARM Linux
2011-04-29 7:59 ` Russell King - ARM Linux
2011-04-29 16:32 ` Jesse Barnes
2011-04-29 16:32 ` Jesse Barnes
2011-04-29 18:29 ` Arnd Bergmann
2011-04-29 18:29 ` Arnd Bergmann
2011-04-29 22:15 ` Russell King - ARM Linux
2011-04-29 22:15 ` Russell King - ARM Linux
2011-05-02 4:42 ` David Brown
2011-05-02 4:42 ` David Brown
2011-05-02 11:26 ` Arnd Bergmann
2011-05-02 11:26 ` Arnd Bergmann
2011-04-29 22:37 ` Benjamin Herrenschmidt
2011-04-29 22:37 ` Benjamin Herrenschmidt
2011-04-29 13:42 ` Joerg Roedel
2011-04-29 13:42 ` Joerg Roedel
2011-04-29 14:19 ` Jerome Glisse
2011-04-29 14:19 ` Jerome Glisse
2011-04-29 15:37 ` Jordan Crouse
2011-04-29 15:37 ` Jordan Crouse
2011-04-28 14:38 ` FUJITA Tomonori
2011-04-28 14:38 ` FUJITA Tomonori
2011-04-29 0:25 ` Benjamin Herrenschmidt
2011-04-29 0:25 ` Benjamin Herrenschmidt
2011-04-29 11:21 ` Arnd Bergmann
2011-04-29 11:21 ` Arnd Bergmann
2011-04-28 10:41 ` Joerg Roedel
2011-04-28 10:41 ` Joerg Roedel
2011-04-28 11:01 ` Russell King - ARM Linux
2011-04-28 11:01 ` Russell King - ARM Linux
2011-04-28 12:25 ` Joerg Roedel
2011-04-28 12:25 ` Joerg Roedel
2011-04-28 12:42 ` Russell King - ARM Linux
2011-04-28 12:42 ` Russell King - ARM Linux
2011-04-28 12:59 ` Joerg Roedel
2011-04-28 12:59 ` Joerg Roedel
2011-04-28 13:02 ` Arnd Bergmann
2011-04-28 13:02 ` Arnd Bergmann
2011-04-28 13:19 ` Russell King - ARM Linux
2011-04-28 13:19 ` Russell King - ARM Linux
2011-04-28 13:56 ` Joerg Roedel
2011-04-28 13:56 ` Joerg Roedel
2011-04-28 14:30 ` Russell King - ARM Linux
2011-04-28 14:30 ` Russell King - ARM Linux
2011-04-27 9:52 ` Catalin Marinas
2011-04-27 9:52 ` Catalin Marinas
2011-04-27 10:43 ` Arnd Bergmann
2011-04-27 10:43 ` Arnd Bergmann
2011-04-27 11:08 ` Catalin Marinas
2011-04-27 11:08 ` Catalin Marinas
2011-04-28 0:15 ` Valdis.Kletnieks
2011-04-28 0:15 ` Valdis.Kletnieks at vt.edu
2011-04-28 8:27 ` Catalin Marinas
2011-04-28 8:27 ` Catalin Marinas
2011-04-28 12:12 ` Arnd Bergmann
2011-04-28 12:12 ` Arnd Bergmann
2011-04-28 12:36 ` Russell King - ARM Linux
2011-04-28 12:36 ` Russell King - ARM Linux
2011-04-28 12:48 ` Arnd Bergmann
2011-04-28 12:48 ` Arnd Bergmann
2011-05-03 14:45 ` Dave Martin
2011-05-03 14:45 ` Dave Martin
2011-04-29 15:41 ` [Linaro-mm-sig] " Arnd Bergmann
2011-04-29 15:41 ` Arnd Bergmann
2011-04-29 16:42 ` Catalin Marinas
2011-04-29 16:42 ` Catalin Marinas
2011-05-03 15:05 ` [Linaro-mm-sig] " Laurent Pinchart
2011-05-03 15:05 ` Laurent Pinchart
2011-05-03 15:31 ` Arnd Bergmann
2011-05-03 15:31 ` Arnd Bergmann
2011-04-27 14:06 ` FUJITA Tomonori
2011-04-27 14:06 ` FUJITA Tomonori
2011-04-27 14:29 ` Catalin Marinas
2011-04-27 14:29 ` Catalin Marinas
2011-04-27 14:34 ` FUJITA Tomonori
2011-04-27 14:34 ` FUJITA Tomonori
2011-04-27 20:29 ` Russell King - ARM Linux
2011-04-27 20:29 ` Russell King - ARM Linux
2011-04-27 21:45 ` Benjamin Herrenschmidt
2011-04-27 21:45 ` Benjamin Herrenschmidt
2011-04-28 7:24 ` [Linaro-mm-sig] " KyongHo Cho
2011-04-28 7:24 ` KyongHo Cho
2011-04-28 8:31 ` Catalin Marinas
2011-04-28 8:31 ` Catalin Marinas
2011-04-27 21:31 ` Benjamin Herrenschmidt
2011-04-27 21:31 ` Benjamin Herrenschmidt
2011-04-28 9:42 ` Russell King - ARM Linux
2011-04-28 9:42 ` Russell King - ARM Linux
2011-04-28 10:27 ` Joerg Roedel
2011-04-28 10:27 ` Joerg Roedel
2011-04-28 12:15 ` Arnd Bergmann
2011-04-28 12:15 ` Arnd Bergmann
2011-05-03 14:35 [Linaro-mm-sig] " Laurent Pinchart
2011-05-03 14:35 ` Laurent Pinchart
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