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15 Sep 2020 23:12:16 +0000 Received: from EX13MTAUEE001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan2.iad.amazon.com [10.40.163.34]) by email-inbound-relay-1d-5dd976cd.us-east-1.amazon.com (Postfix) with ESMTPS id 49F02A21FC; Tue, 15 Sep 2020 23:12:15 +0000 (UTC) Received: from EX13D33UEE002.ant.amazon.com (10.43.62.233) by EX13MTAUEE001.ant.amazon.com (10.43.62.226) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 15 Sep 2020 23:12:14 +0000 Received: from EX13MTAUEE002.ant.amazon.com (10.43.62.24) by EX13D33UEE002.ant.amazon.com (10.43.62.233) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 15 Sep 2020 23:12:14 +0000 Received: from dev-dsk-csbisa-2a-37939146.us-west-2.amazon.com (172.19.34.216) by mail-relay.amazon.com (10.43.62.224) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Tue, 15 Sep 2020 23:12:14 +0000 Received: by dev-dsk-csbisa-2a-37939146.us-west-2.amazon.com (Postfix, from userid 800212) id 44DF4258; Tue, 15 Sep 2020 23:12:13 +0000 (UTC) Date: Tue, 15 Sep 2020 23:12:13 +0000 From: Clint Sbisa To: Benjamin Herrenschmidt Subject: Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs Message-ID: <20200915231213.7bjywegoccohpcop@amazon.com> References: <20200911214225.hml2wbbq2rofn4re@amazon.com> <20200914141726.GA904879@nvidia.com> <20200914142406.k44zrnp2wdsandsp@amazon.com> <20200914143819.GC904879@nvidia.com> <375c478593945a416f3180c3773bcb5240d2e36c.camel@kernel.crashing.org> <1d6f2ceb8d3538c906a1fdb8cd3d4c74ccffa42e.camel@kernel.crashing.org> <20200914225740.GP904879@nvidia.com> <2b539df4c9ec703458e46da2fc879ee3b310b31c.camel@kernel.crashing.org> <20200915101831.GA2616@e121166-lin.cambridge.arm.com> <28c9039eba4bc288abb8ab1b82b51c16023fcb3c.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <28c9039eba4bc288abb8ab1b82b51c16023fcb3c.camel@kernel.crashing.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200915_191222_388311_D6799860 X-CRM114-Status: GOOD ( 30.70 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Lorenzo Pieralisi , Leon Romanovsky , linux-pci@vger.kernel.org, Bjorn Helgaas , Jason Gunthorpe , catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel