From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B48CC433E2 for ; Tue, 15 Sep 2020 23:12:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 110D021D24 for ; Tue, 15 Sep 2020 23:12:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="D06KEDCV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727465AbgIOXMZ (ORCPT ); Tue, 15 Sep 2020 19:12:25 -0400 Received: from smtp-fw-9102.amazon.com ([207.171.184.29]:61030 "EHLO smtp-fw-9102.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727139AbgIOXMU (ORCPT ); Tue, 15 Sep 2020 19:12:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1600211540; x=1631747540; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=/cVEHufwAE8Pz5l6vDgyGmqUjuh+y4B65zCp+5zWJdA=; b=D06KEDCVdwmMJ6DI3TGkQWQMS/7iyMAHLtwsO+yzs0bAJMa7HMUJzAIv REEftxGzQ0oQlRAlGHBegQqypbvs20l9OU/Bc+Sa07L7Wyke7CiGpl+cX lmovlLB2udP2F7qSPjGK8w1Djhgjq6RTW3/XMu+btIz0tRguy02iBjiuj I=; X-IronPort-AV: E=Sophos;i="5.76,430,1592870400"; d="scan'208";a="76467983" Received: from sea32-co-svc-lb4-vlan3.sea.corp.amazon.com (HELO email-inbound-relay-1d-5dd976cd.us-east-1.amazon.com) ([10.47.23.38]) by smtp-border-fw-out-9102.sea19.amazon.com with ESMTP; 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 CC: Lorenzo Pieralisi , Jason Gunthorpe , , Bjorn Helgaas , , , , Leon Romanovsky 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-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <28c9039eba4bc288abb8ab1b82b51c16023fcb3c.camel@kernel.crashing.org> Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.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