From: Catalin Marinas <catalin.marinas@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
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 09:48:52 +0100 [thread overview]
Message-ID: <20200916084851.GA3122@gaia> (raw)
In-Reply-To: <20200916083315.GC27496@willie-the-truck>
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:
> > > On Tue, 2020-09-15 at 08:05 -0300, Jason Gunthorpe wrote:
> > > > > To sum it up:
> > > > >
> > > > > (1) RDMA drivers need a new mapping function/attribute to define their
> > > > > message push model. Actually the message model is not necessarily related
> > > > > to write combining a la x86, so we should probably come up with a better
> > > > > and consistent naming. Enabling this patchset may trigger performance
> > > > > regressions on mellanox drivers on arm64 - this ought to be
> > > > > addressed.
> > > >
> > > > It is pretty clear now that the certain ARM chips that don't do write
> > > > combining with pgprot_writecombine will performance regress if they
> > > > are running a certain uncommon Mellanox configuration. I suspect these
> > > > deployments are all running the out of tree patch for DEVICE_GRE
> > > > though.
> > >
> > > I'm not sure I understand...
> > >
> > > Today those ARM chips will not use pgprot_writecombine (at least not
> > > using that code path, they might still use it as the result of the
> > > other path in the driver that can enable it).
> >
> > Not quite, upstream kernel will never use WC on those
> > devices. DEVICE_GRE is not supported in upstream,
> > arch_can_pci_mmap_wc() is always false and the WC tester will always
> > fail.
> >
> > > 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.
--
Catalin
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Leon Romanovsky <leon@kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Bjorn Helgaas <helgaas@kernel.org>,
Jason Gunthorpe <jgg@nvidia.com>,
linux-pci@vger.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 09:48:52 +0100 [thread overview]
Message-ID: <20200916084851.GA3122@gaia> (raw)
In-Reply-To: <20200916083315.GC27496@willie-the-truck>
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:
> > > On Tue, 2020-09-15 at 08:05 -0300, Jason Gunthorpe wrote:
> > > > > To sum it up:
> > > > >
> > > > > (1) RDMA drivers need a new mapping function/attribute to define their
> > > > > message push model. Actually the message model is not necessarily related
> > > > > to write combining a la x86, so we should probably come up with a better
> > > > > and consistent naming. Enabling this patchset may trigger performance
> > > > > regressions on mellanox drivers on arm64 - this ought to be
> > > > > addressed.
> > > >
> > > > It is pretty clear now that the certain ARM chips that don't do write
> > > > combining with pgprot_writecombine will performance regress if they
> > > > are running a certain uncommon Mellanox configuration. I suspect these
> > > > deployments are all running the out of tree patch for DEVICE_GRE
> > > > though.
> > >
> > > I'm not sure I understand...
> > >
> > > Today those ARM chips will not use pgprot_writecombine (at least not
> > > using that code path, they might still use it as the result of the
> > > other path in the driver that can enable it).
> >
> > Not quite, upstream kernel will never use WC on those
> > devices. DEVICE_GRE is not supported in upstream,
> > arch_can_pci_mmap_wc() is always false and the WC tester will always
> > fail.
> >
> > > 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.
--
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 8:48 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 [this message]
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
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=20200916084851.GA3122@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.