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From: Clint Sbisa <csbisa@amazon.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Leon Romanovsky <leon@kernel.org>,
	linux-pci@vger.kernel.org, Bjorn Helgaas <helgaas@kernel.org>,
	Jason Gunthorpe <jgg@nvidia.com>,
	catalin.marinas@arm.com, will@kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs
Date: Tue, 15 Sep 2020 23:12:13 +0000	[thread overview]
Message-ID: <20200915231213.7bjywegoccohpcop@amazon.com> (raw)
In-Reply-To: <28c9039eba4bc288abb8ab1b82b51c16023fcb3c.camel@kernel.crashing.org>

On Wed, Sep 16, 2020 at 09:00:09AM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2020-09-15 at 11:18 +0100, Lorenzo Pieralisi 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.
> 
> I doubt it. Besides Mellanox will probably enable WC already through
> the other code path (the use of this accessor is only one of the path
> that enables the driver to do WC).
> 
> I don't think we need to solve the RDMA semantics issue that urgently
> TBH, and it's definitely an orthogonal issue to that at hand.
> 
> > (2) User-space/passthrough drivers rely on VFIO for BAR mappings. Since
> >     it looks relevant, WC message model semantics should be introduced
> >     there, somehow.
> 
> Yes.

I will ping some folks on the VFIO patch to see if we can get the ball rolling
there again.

> 
> > (3) Given the above, the sysfs interface can be enabled. I still don't
> >     see the advantages (other than saying it is there for other arches, ie
> >     what can you really do with the sysfs mappings - see Jason's VFIO/DMA
> >     query) but we can do it. Still, I am not happy about the possible
> >     mellanox regressions - that should be tested/verified before this
> >     patch is merged IMHO. Do we really need it for v5.10 ?
> 
> I don't think there's a significant risk of regression, but then I also
> dont' have a way to test :-)

I'm going to re-submit this patch to Catalin and Will with an updated commit
message capturing the context from this discussion (and cc everyone involved).

As for the whole device GRE / new naming context-- I'll have to defer to
Lorenzo on suggested next steps on this front.

Thanks,
Clint

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  reply	other threads:[~2020-09-15 23:13 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
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 [this message]
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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