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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 A84D8C433F5 for ; Mon, 3 Sep 2018 22:27:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4DE2320862 for ; Mon, 3 Sep 2018 22:27:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4DE2320862 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=deltatee.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726212AbeIDCtK (ORCPT ); Mon, 3 Sep 2018 22:49:10 -0400 Received: from ale.deltatee.com ([207.54.116.67]:38918 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725955AbeIDCtK (ORCPT ); Mon, 3 Sep 2018 22:49:10 -0400 Received: from s0106602ad0811846.cg.shawcable.net ([68.147.191.165] helo=[192.168.0.18]) by ale.deltatee.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.89) (envelope-from ) id 1fwxIo-0006QC-HP; Mon, 03 Sep 2018 16:26:35 -0600 To: Christoph Hellwig , Jens Axboe Cc: linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, Stephen Bates , Keith Busch , Sagi Grimberg , Bjorn Helgaas , Jason Gunthorpe , Max Gurtovoy , Dan Williams , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Benjamin Herrenschmidt , Alex Williamson , =?UTF-8?Q?Christian_K=c3=b6nig?= References: <20180830185352.3369-1-logang@deltatee.com> <20180830185352.3369-8-logang@deltatee.com> <20180901082812.GB670@lst.de> From: Logan Gunthorpe Message-ID: <5f79c012-c6e1-56bb-62fd-0689181fb2c9@deltatee.com> Date: Mon, 3 Sep 2018 16:26:27 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180901082812.GB670@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 68.147.191.165 X-SA-Exim-Rcpt-To: christian.koenig@amd.com, alex.williamson@redhat.com, benh@kernel.crashing.org, jglisse@redhat.com, dan.j.williams@intel.com, maxg@mellanox.com, jgg@mellanox.com, bhelgaas@google.com, sagi@grimberg.me, keith.busch@intel.com, sbates@raithlin.com, linux-block@vger.kernel.org, linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, axboe@kernel.dk, hch@lst.de X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and check support for requests X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/09/18 02:28 AM, Christoph Hellwig wrote: > On Thu, Aug 30, 2018 at 01:11:18PM -0600, Jens Axboe wrote: >> I think this belongs in the caller - both the validity check, and >> passing in NOMERGE for this type of request. I don't want to impose >> this overhead on everything, for a pretty niche case. > > It is just a single branch, which will be predicted as not taken > for non-P2P users. The benefit is that we get proper error checking > by doing it in the block code. I personally agree with Christoph. But if there's consensus in the other direction or this is a real blocker moving this forward, I can remove it for the next version. Logan