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From: Logan Gunthorpe <logang@deltatee.com>
To: Jason Gunthorpe <jgg@ziepe.ca>, Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-pci@vger.kernel.org,
	linux-rdma <linux-rdma@vger.kernel.org>,
	Jens Axboe <axboe@kernel.dk>, Bjorn Helgaas <bhelgaas@google.com>,
	Sagi Grimberg <sagi@grimberg.me>, Keith Busch <kbusch@kernel.org>,
	Stephen Bates <sbates@raithlin.com>
Subject: Re: [RFC PATCH 00/28] Removing struct page from P2PDMA
Date: Mon, 24 Jun 2019 10:53:38 -0600	[thread overview]
Message-ID: <7210ba39-c923-79ca-57bb-7cf9afe21d54@deltatee.com> (raw)
In-Reply-To: <20190624135550.GB8268@ziepe.ca>



On 2019-06-24 7:55 a.m., Jason Gunthorpe wrote:
> On Mon, Jun 24, 2019 at 03:50:24PM +0200, Christoph Hellwig wrote:
>> On Mon, Jun 24, 2019 at 10:46:41AM -0300, Jason Gunthorpe wrote:
>>> BTW, it is not just offset right? It is possible that the IOMMU can
>>> generate unique dma_addr_t values for each device?? Simple offset is
>>> just something we saw in certain embedded cases, IIRC.
>>
>> Yes, it could.  If we are trying to do P2P between two devices on
>> different root ports and with the IOMMU enabled we'll generate
>> a new bus address for the BAR on the other side dynamically everytime
>> we map.
> 
> Even with the same root port if ACS is turned on could behave like this.

Yup.

> It is only a very narrow case where you can take shortcuts with
> dma_addr_t, and I don't think shortcuts like are are appropriate for
> the mainline kernel..

I don't think it's that narrow and it opens up a lot of avenues for
system design that people are wanting to go. If your high speed data
path can avoid the root complex and CPU, you can design a system which a
much smaller CPU and fewer lanes directed at the CPU.

Logan

  reply	other threads:[~2019-06-24 16:53 UTC|newest]

Thread overview: 89+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-20 16:12 [RFC PATCH 00/28] Removing struct page from P2PDMA Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 01/28] block: Introduce DMA direct request type Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 02/28] block: Add dma_vec structure Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 03/28] block: Warn on mis-use of dma-direct bios Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 04/28] block: Never bounce " Logan Gunthorpe
2019-06-20 17:23   ` Jason Gunthorpe
2019-06-20 18:38     ` Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 05/28] block: Skip dma-direct bios in bio_integrity_prep() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 06/28] block: Support dma-direct bios in bio_advance_iter() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 07/28] block: Use dma_vec length in bio_cur_bytes() for dma-direct bios Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 08/28] block: Introduce dmavec_phys_mergeable() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 09/28] block: Introduce vec_gap_to_prev() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 10/28] block: Create generic vec_split_segs() from bvec_split_segs() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 11/28] block: Create blk_segment_split_ctx Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 12/28] block: Create helper for bvec_should_split() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 13/28] block: Generalize bvec_should_split() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 14/28] block: Support splitting dma-direct bios Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 15/28] block: Support counting dma-direct bio segments Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 16/28] block: Implement mapping dma-direct requests to SGs in blk_rq_map_sg() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 17/28] block: Introduce queue flag to indicate support for dma-direct bios Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 18/28] block: Introduce bio_add_dma_addr() Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 19/28] nvme-pci: Support dma-direct bios Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 20/28] IB/core: Introduce API for initializing a RW ctx from a DMA address Logan Gunthorpe
2019-06-20 16:49   ` Jason Gunthorpe
2019-06-20 16:59     ` Logan Gunthorpe
2019-06-20 17:11       ` Jason Gunthorpe
2019-06-20 18:24         ` Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 21/28] nvmet: Split nvmet_bdev_execute_rw() into a helper function Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 22/28] nvmet: Use DMA addresses instead of struct pages for P2P Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 23/28] nvme-pci: Remove support for PCI_P2PDMA requests Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 24/28] block: Remove PCI_P2PDMA queue flag Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 25/28] IB/core: Remove P2PDMA mapping support in rdma_rw_ctx Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 26/28] PCI/P2PDMA: Remove SGL helpers Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 27/28] PCI/P2PDMA: Remove struct pages that back P2PDMA memory Logan Gunthorpe
2019-06-20 16:12 ` [RFC PATCH 28/28] memremap: Remove PCI P2PDMA page memory type Logan Gunthorpe
2019-06-20 18:45 ` [RFC PATCH 00/28] Removing struct page from P2PDMA Dan Williams
2019-06-20 19:33   ` Jason Gunthorpe
2019-06-20 20:18     ` Dan Williams
2019-06-20 20:51       ` Logan Gunthorpe
2019-06-21 17:47       ` Jason Gunthorpe
2019-06-21 17:54         ` Dan Williams
2019-06-24  7:31     ` Christoph Hellwig
2019-06-24 13:46       ` Jason Gunthorpe
2019-06-24 13:50         ` Christoph Hellwig
2019-06-24 13:55           ` Jason Gunthorpe
2019-06-24 16:53             ` Logan Gunthorpe [this message]
2019-06-24 18:16               ` Jason Gunthorpe
2019-06-24 18:28                 ` Logan Gunthorpe
2019-06-24 18:54                   ` Jason Gunthorpe
2019-06-24 19:37                     ` Logan Gunthorpe
2019-06-24 16:10         ` Logan Gunthorpe
2019-06-25  7:18           ` Christoph Hellwig
2019-06-20 19:34   ` Logan Gunthorpe
2019-06-20 23:40     ` Dan Williams
2019-06-20 23:42       ` Logan Gunthorpe
2019-06-24  7:27 ` Christoph Hellwig
2019-06-24 16:07   ` Logan Gunthorpe
2019-06-25  7:20     ` Christoph Hellwig
2019-06-25 15:57       ` Logan Gunthorpe
2019-06-25 17:01         ` Christoph Hellwig
2019-06-25 19:54           ` Logan Gunthorpe
2019-06-26  6:57             ` Christoph Hellwig
2019-06-26 18:31               ` Logan Gunthorpe
2019-06-26 20:21                 ` Jason Gunthorpe
2019-06-26 20:39                   ` Dan Williams
2019-06-26 20:54                     ` Jason Gunthorpe
2019-06-26 20:55                     ` Logan Gunthorpe
2019-06-26 20:45                   ` Logan Gunthorpe
2019-06-26 21:00                     ` Jason Gunthorpe
2019-06-26 21:18                       ` Logan Gunthorpe
2019-06-27  6:32                         ` Jason Gunthorpe
2019-06-27 16:09                           ` Logan Gunthorpe
2019-06-27 16:35                             ` Jason Gunthorpe
2019-06-27 16:49                               ` Logan Gunthorpe
2019-06-28  4:57                                 ` Jason Gunthorpe
2019-06-28 16:22                                   ` Logan Gunthorpe
2019-06-28 17:29                                     ` Jason Gunthorpe
2019-06-28 18:29                                       ` Logan Gunthorpe
2019-06-28 19:09                                         ` Jason Gunthorpe
2019-06-28 19:35                                           ` Logan Gunthorpe
2019-07-02 22:45                                             ` Jason Gunthorpe
2019-07-02 22:52                                               ` Logan Gunthorpe
2019-06-27  9:08                     ` Christoph Hellwig
2019-06-27 16:30                       ` Logan Gunthorpe
2019-06-27 17:00                         ` Christoph Hellwig
2019-06-27 18:00                           ` Logan Gunthorpe
2019-06-28 13:38                             ` Christoph Hellwig
2019-06-28 15:54                               ` Logan Gunthorpe
2019-06-27  9:01                 ` Christoph Hellwig

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