From: Jason Gunthorpe <jgg@nvidia.com>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: catalin.marinas@arm.com, Leon Romanovsky <leon@kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Bjorn Helgaas <helgaas@kernel.org>,
linux-pci@vger.kernel.org, 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: Tue, 15 Sep 2020 08:05:11 -0300 [thread overview]
Message-ID: <20200915110511.GQ904879@nvidia.com> (raw)
In-Reply-To: <20200915101831.GA2616@e121166-lin.cambridge.arm.com>
On Tue, Sep 15, 2020 at 11:18:31AM +0100, Lorenzo Pieralisi wrote:
> On Tue, Sep 15, 2020 at 09:25:57AM +1000, Benjamin Herrenschmidt wrote:
> > On Mon, 2020-09-14 at 19:57 -0300, Jason Gunthorpe wrote:
> > > On Tue, Sep 15, 2020 at 08:00:27AM +1000, Benjamin Herrenschmidt wrote:
> > > > On Tue, 2020-09-15 at 07:42 +1000, Benjamin Herrenschmidt wrote:
> > > > >
> > > > > > which is back to my original question, how do you do DMA using
> > > > > > /sys/xx/resources? Why not use VFIO like everything else?
> > > > >
> > > > > Note: All this doesnt' change the fact that sys/xx/resources_wc
> > > > > exists
> > > > > for other archs and I see no reasons so far not to have it on ARM...
> > > >
> > > > Also... it looks like VFIO also doesn't provide a way to do WC yet
> > > > unfortunately :-(
> > >
> > > Yes, but if the driving reason for this patch is because a VFIO user
> > > like EFA DPDK is trying to work around VFIO limitations, then I'd say
> > > the VFIO mmap should be amended, and not so much worring about sysfs.
> >
> > I don't think the two are exclusive.
> >
> > > While there is no reason for ARM to not show the sysfs, it really
> > > should never be used. Modern kernels in secure boot don't even show
> > > it, for instance.
> >
> > It's useful for random things, I've used it quite a bit in a previous
> > life for things like in-lab hw testing etc... There's tooling out
> > there, esp. in the more 'embedded' side of thing that uses this, I
> > don't see a good reason not to provide the same level of functionality.
> >
> > So Lorenzo, imho, we should merge the patch.
>
> 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.
So, I wouldn't worry about it - but would prefer to see ARM folks
advance some proposal to accommodate those chips that need DEVICE_GRE.
Jason
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next prev parent reply other threads:[~2020-09-15 11:14 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200831151827.pumm2p54fyj7fz5s@amazon.com>
[not found] ` <20200902113207.GA27676@e121166-lin.cambridge.arm.com>
[not found] ` <20200902142922.xc4x6m33unkzewuh@amazon.com>
2020-09-02 16:47 ` [PATCH] arm64: Enable PCI write-combine resources under sysfs Lorenzo Pieralisi
2020-09-02 17:21 ` Catalin Marinas
2020-09-02 17:54 ` Lorenzo Pieralisi
2020-09-02 23:03 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:08 ` Benjamin Herrenschmidt
2020-09-02 23:07 ` Benjamin Herrenschmidt
2020-09-03 11:08 ` Lorenzo Pieralisi
2020-09-03 14:36 ` Clint Sbisa
2020-09-03 22:26 ` Benjamin Herrenschmidt
2020-09-07 23:33 ` Benjamin Herrenschmidt
2020-09-10 9:46 ` Lorenzo Pieralisi
2020-09-10 10:54 ` Leon Romanovsky
2020-09-10 12:37 ` Jason Gunthorpe
2020-09-10 15:17 ` Lorenzo Pieralisi
2020-09-10 17:10 ` Jason Gunthorpe
2020-09-10 21:46 ` Benjamin Herrenschmidt
2020-09-10 23:29 ` Jason Gunthorpe
2020-09-11 0:39 ` Benjamin Herrenschmidt
2020-09-11 14:21 ` Jason Gunthorpe
2020-09-11 21:42 ` Clint Sbisa
2020-09-14 14:17 ` Jason Gunthorpe
2020-09-14 14:24 ` Clint Sbisa
2020-09-14 14:38 ` Jason Gunthorpe
2020-09-14 21:42 ` Benjamin Herrenschmidt
2020-09-14 22:00 ` Benjamin Herrenschmidt
2020-09-14 22:32 ` Clint Sbisa
2020-09-14 22:57 ` Jason Gunthorpe
2020-09-14 23:25 ` Benjamin Herrenschmidt
2020-09-15 10:18 ` Lorenzo Pieralisi
2020-09-15 11:05 ` Jason Gunthorpe [this message]
2020-09-15 23:17 ` Benjamin Herrenschmidt
2020-09-15 23:40 ` Jason Gunthorpe
2020-09-16 7:59 ` Benjamin Herrenschmidt
2020-09-16 12:12 ` Jason Gunthorpe
2020-09-16 14:09 ` Lorenzo Pieralisi
2020-09-16 14:14 ` Jason Gunthorpe
2020-09-16 23:59 ` Benjamin Herrenschmidt
2020-09-17 10:28 ` Lorenzo Pieralisi
2020-09-17 11:32 ` Jason Gunthorpe
2020-09-17 14:01 ` Lorenzo Pieralisi
2020-09-17 16:08 ` Will Deacon
2020-09-16 12:48 ` Leon Romanovsky
2020-09-16 8:33 ` Will Deacon
2020-09-16 8:48 ` Catalin Marinas
2020-09-16 14:15 ` Lorenzo Pieralisi
2020-09-16 17:00 ` Catalin Marinas
2020-09-16 21:29 ` Benjamin Herrenschmidt
2020-09-16 12:08 ` Jason Gunthorpe
2020-09-15 23:00 ` Benjamin Herrenschmidt
2020-09-15 23:12 ` Clint Sbisa
2020-09-14 21:41 ` Benjamin Herrenschmidt
2020-08-21 15:51 Clint Sbisa
2020-08-27 14:41 ` Clint Sbisa
2020-08-31 15:22 ` Clint Sbisa
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