From: Catalin Marinas <catalin.marinas@arm.com>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Will Deacon <will@kernel.org>, Jason Gunthorpe <jgg@nvidia.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Clint Sbisa <csbisa@amazon.com>,
linux-pci@vger.kernel.org, Bjorn Helgaas <helgaas@kernel.org>,
linux-arm-kernel@lists.infradead.org,
Leon Romanovsky <leon@kernel.org>
Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs
Date: Wed, 16 Sep 2020 18:00:59 +0100 [thread overview]
Message-ID: <20200916170058.GD3122@gaia> (raw)
In-Reply-To: <20200916141502.GB20770@e121166-lin.cambridge.arm.com>
On Wed, Sep 16, 2020 at 03:15:02PM +0100, Lorenzo Pieralisi wrote:
> On Wed, Sep 16, 2020 at 09:48:52AM +0100, Catalin Marinas wrote:
> > On Wed, Sep 16, 2020 at 09:33:16AM +0100, Will Deacon wrote:
> > > On Tue, Sep 15, 2020 at 08:40:06PM -0300, Jason Gunthorpe wrote:
> > > > On Wed, Sep 16, 2020 at 09:17:38AM +1000, Benjamin Herrenschmidt wrote:
> > > > > With the patch, those device will now use MT_DEVICE_NC.
> > > >
> > > > Which doesn't do WC at all on some ARM implementations.
> > >
> > > Is that just TX2? I remember that thing being weird where GRE performed
> > > better than NC, but I thought that was a one off (and the thing is dead).
> >
> > I recall something along these lines. Hopefully ARM updated the guidance
> > to licensees.
> >
> > > NC is more permissive than GRE, so I think that's the right one to use; i.e.
> > > we go for the fewest number of restrictions on the hardware. If somebody
> > > screws up the uarch, that's up to them.
> >
> > I agree, Normal NC is better as long as the BAR can tolerate read
> > side-effects.
>
> That we don't know but if a prefetchable BAR can't tolerate read
> side effects this would be already a problem on eg x86 - that's
> the best we can hope for given the current PCI specs.
>
> +1 on normal NC. The only open point is whether we should make
> arch_can_pci_mmap_wc() return false on platforms like TX2.
I lost track in this thread whether it matters. TX2 would need Device
GRE for optimal performance but the kernel doesn't currently provide it
anyway. We could expose a new memory type, aligned_wc ;).
--
Catalin
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Leon Romanovsky <leon@kernel.org>,
linux-pci@vger.kernel.org, Bjorn Helgaas <helgaas@kernel.org>,
Jason Gunthorpe <jgg@nvidia.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org,
Clint Sbisa <csbisa@amazon.com>
Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs
Date: Wed, 16 Sep 2020 18:00:59 +0100 [thread overview]
Message-ID: <20200916170058.GD3122@gaia> (raw)
In-Reply-To: <20200916141502.GB20770@e121166-lin.cambridge.arm.com>
On Wed, Sep 16, 2020 at 03:15:02PM +0100, Lorenzo Pieralisi wrote:
> On Wed, Sep 16, 2020 at 09:48:52AM +0100, Catalin Marinas wrote:
> > On Wed, Sep 16, 2020 at 09:33:16AM +0100, Will Deacon wrote:
> > > On Tue, Sep 15, 2020 at 08:40:06PM -0300, Jason Gunthorpe wrote:
> > > > On Wed, Sep 16, 2020 at 09:17:38AM +1000, Benjamin Herrenschmidt wrote:
> > > > > With the patch, those device will now use MT_DEVICE_NC.
> > > >
> > > > Which doesn't do WC at all on some ARM implementations.
> > >
> > > Is that just TX2? I remember that thing being weird where GRE performed
> > > better than NC, but I thought that was a one off (and the thing is dead).
> >
> > I recall something along these lines. Hopefully ARM updated the guidance
> > to licensees.
> >
> > > NC is more permissive than GRE, so I think that's the right one to use; i.e.
> > > we go for the fewest number of restrictions on the hardware. If somebody
> > > screws up the uarch, that's up to them.
> >
> > I agree, Normal NC is better as long as the BAR can tolerate read
> > side-effects.
>
> That we don't know but if a prefetchable BAR can't tolerate read
> side effects this would be already a problem on eg x86 - that's
> the best we can hope for given the current PCI specs.
>
> +1 on normal NC. The only open point is whether we should make
> arch_can_pci_mmap_wc() return false on platforms like TX2.
I lost track in this thread whether it matters. TX2 would need Device
GRE for optimal performance but the kernel doesn't currently provide it
anyway. We could expose a new memory type, aligned_wc ;).
--
Catalin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-09-16 20:48 UTC|newest]
Thread overview: 117+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 15:18 [PATCH] arm64: Enable PCI write-combine resources under sysfs Clint Sbisa
2020-08-31 23:24 ` Benjamin Herrenschmidt
2020-09-01 18:37 ` Bjorn Helgaas
2020-09-01 23:22 ` Benjamin Herrenschmidt
2020-09-02 8:57 ` Will Deacon
2020-09-02 11:32 ` Lorenzo Pieralisi
2020-09-02 14:29 ` Clint Sbisa
2020-09-02 16:47 ` Lorenzo Pieralisi
2020-09-02 16:47 ` Lorenzo Pieralisi
2020-09-02 17:21 ` Catalin Marinas
2020-09-02 17:21 ` Catalin Marinas
2020-09-02 17:54 ` Lorenzo Pieralisi
2020-09-02 17:54 ` Lorenzo Pieralisi
2020-09-02 23:03 ` Benjamin Herrenschmidt
2020-09-02 23:03 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:07 ` Benjamin Herrenschmidt
2020-09-02 23:07 ` Benjamin Herrenschmidt
2020-09-03 11:08 ` Lorenzo Pieralisi
2020-09-03 11:08 ` Lorenzo Pieralisi
2020-09-03 14:36 ` Clint Sbisa
2020-09-03 14:36 ` Clint Sbisa
2020-09-03 22:26 ` Benjamin Herrenschmidt
2020-09-03 22:26 ` Benjamin Herrenschmidt
2020-09-07 23:33 ` Benjamin Herrenschmidt
2020-09-07 23:33 ` Benjamin Herrenschmidt
2020-09-10 9:46 ` Lorenzo Pieralisi
2020-09-10 9:46 ` Lorenzo Pieralisi
2020-09-10 10:54 ` Leon Romanovsky
2020-09-10 10:54 ` Leon Romanovsky
2020-09-10 12:37 ` Jason Gunthorpe
2020-09-10 12:37 ` Jason Gunthorpe
2020-09-10 15:17 ` Lorenzo Pieralisi
2020-09-10 15:17 ` Lorenzo Pieralisi
2020-09-10 17:10 ` Jason Gunthorpe
2020-09-10 17:10 ` Jason Gunthorpe
2020-09-10 21:46 ` Benjamin Herrenschmidt
2020-09-10 21:46 ` Benjamin Herrenschmidt
2020-09-10 23:29 ` Jason Gunthorpe
2020-09-10 23:29 ` Jason Gunthorpe
2020-09-11 0:39 ` Benjamin Herrenschmidt
2020-09-11 0:39 ` Benjamin Herrenschmidt
2020-09-11 14:21 ` Jason Gunthorpe
2020-09-11 14:21 ` Jason Gunthorpe
2020-09-11 21:42 ` Clint Sbisa
2020-09-11 21:42 ` Clint Sbisa
2020-09-14 14:17 ` Jason Gunthorpe
2020-09-14 14:17 ` Jason Gunthorpe
2020-09-14 14:24 ` Clint Sbisa
2020-09-14 14:24 ` Clint Sbisa
2020-09-14 14:38 ` Jason Gunthorpe
2020-09-14 14:38 ` Jason Gunthorpe
2020-09-14 21:42 ` Benjamin Herrenschmidt
2020-09-14 21:42 ` Benjamin Herrenschmidt
2020-09-14 22:00 ` Benjamin Herrenschmidt
2020-09-14 22:00 ` Benjamin Herrenschmidt
2020-09-14 22:32 ` Clint Sbisa
2020-09-14 22:32 ` Clint Sbisa
2020-09-14 22:57 ` Jason Gunthorpe
2020-09-14 22:57 ` Jason Gunthorpe
2020-09-14 23:25 ` Benjamin Herrenschmidt
2020-09-14 23:25 ` Benjamin Herrenschmidt
2020-09-15 10:18 ` Lorenzo Pieralisi
2020-09-15 10:18 ` Lorenzo Pieralisi
2020-09-15 11:05 ` Jason Gunthorpe
2020-09-15 11:05 ` Jason Gunthorpe
2020-09-15 23:17 ` Benjamin Herrenschmidt
2020-09-15 23:17 ` Benjamin Herrenschmidt
2020-09-15 23:40 ` Jason Gunthorpe
2020-09-15 23:40 ` Jason Gunthorpe
2020-09-16 7:59 ` Benjamin Herrenschmidt
2020-09-16 7:59 ` Benjamin Herrenschmidt
2020-09-16 12:12 ` Jason Gunthorpe
2020-09-16 12:12 ` Jason Gunthorpe
2020-09-16 14:09 ` Lorenzo Pieralisi
2020-09-16 14:09 ` Lorenzo Pieralisi
2020-09-16 14:14 ` Jason Gunthorpe
2020-09-16 14:14 ` Jason Gunthorpe
2020-09-16 23:59 ` Benjamin Herrenschmidt
2020-09-16 23:59 ` Benjamin Herrenschmidt
2020-09-17 10:28 ` Lorenzo Pieralisi
2020-09-17 10:28 ` Lorenzo Pieralisi
2020-09-17 11:32 ` Jason Gunthorpe
2020-09-17 11:32 ` Jason Gunthorpe
2020-09-17 14:01 ` Lorenzo Pieralisi
2020-09-17 14:01 ` Lorenzo Pieralisi
2020-09-17 16:08 ` Will Deacon
2020-09-17 16:08 ` Will Deacon
2020-09-16 12:48 ` Leon Romanovsky
2020-09-16 12:48 ` Leon Romanovsky
2020-09-16 8:33 ` Will Deacon
2020-09-16 8:33 ` Will Deacon
2020-09-16 8:48 ` Catalin Marinas
2020-09-16 8:48 ` Catalin Marinas
2020-09-16 14:15 ` Lorenzo Pieralisi
2020-09-16 14:15 ` Lorenzo Pieralisi
2020-09-16 17:00 ` Catalin Marinas [this message]
2020-09-16 17:00 ` Catalin Marinas
2020-09-16 21:29 ` Benjamin Herrenschmidt
2020-09-16 21:29 ` Benjamin Herrenschmidt
2020-09-16 12:08 ` Jason Gunthorpe
2020-09-16 12:08 ` Jason Gunthorpe
2020-09-15 23:00 ` Benjamin Herrenschmidt
2020-09-15 23:00 ` Benjamin Herrenschmidt
2020-09-15 23:12 ` Clint Sbisa
2020-09-15 23:12 ` Clint Sbisa
2020-09-14 21:41 ` Benjamin Herrenschmidt
2020-09-14 21:41 ` Benjamin Herrenschmidt
-- strict thread matches above, loose matches on Subject: below --
2020-08-21 15:51 Clint Sbisa
2020-08-21 15:51 ` Clint Sbisa
2020-08-27 14:41 ` Clint Sbisa
2020-08-27 14:41 ` Clint Sbisa
2020-08-31 15:22 ` Clint Sbisa
2020-08-31 15:22 ` Clint Sbisa
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200916170058.GD3122@gaia \
--to=catalin.marinas@arm.com \
--cc=benh@kernel.crashing.org \
--cc=csbisa@amazon.com \
--cc=helgaas@kernel.org \
--cc=jgg@nvidia.com \
--cc=leon@kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-pci@vger.kernel.org \
--cc=lorenzo.pieralisi@arm.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.