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From: Logan Gunthorpe <logang@deltatee.com>
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Bjorn Helgaas <helgaas@kernel.org>,
	Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	"James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Jens Axboe <axboe@kernel.dk>,
	Steve Wise <swise@opengridcomputing.com>,
	Stephen Bates <sbates@raithlin.com>,
	Max Gurtovoy <maxg@mellanox.com>,
	Keith Busch <keith.busch@intel.com>,
	linux-pci@vger.kernel.org,
	linux-scsi <linux-scsi@vger.kernel.org>,
	linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org,
	linux-nvdimm <linux-nvdimm@ml01.01.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Jerome Glisse <jglisse@redhat.com>
Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
Date: Wed, 19 Apr 2017 13:02:49 -0600	[thread overview]
Message-ID: <21e8099a-d19d-7df0-682d-627d8b81dfde@deltatee.com> (raw)
In-Reply-To: <20170419183247.GA13716@obsidianresearch.com>



On 19/04/17 12:32 PM, Jason Gunthorpe wrote:
> On Wed, Apr 19, 2017 at 12:01:39PM -0600, Logan Gunthorpe wrote:
> Not entirely, it would have to call through the whole process
> including the arch_p2p_cross_segment()..

Hmm, yes. Though it's still not clear what, if anything,
arch_p2p_cross_segment would be doing. In my experience, if you are
going between host bridges, the CPU address (or PCI address -- I'm not
sure which seeing they are the same on my system) would still work fine
-- it just _may_ be a bad idea because of performance.

Similarly if you are crossing via a QPI bus or similar, I'd expect the
CPU address to work fine. But here the performance is even less likely
to be any good.


>          // Try the arch specific helper
> 	 const struct dma_map_ops *comp_ops = get_dma_ops(completer);
> 	 const struct dma_map_ops *init_ops = get_dma_ops(initiator);

So, in this case, what device does the completer point to? The PCI
device or a more specific GPU device? If it's the former, who's
responsible for setting the new dma_ops? Typically the dma_ops are arch
specific but now you'd be adding ones that are tied to hmm or the gpu.

>> I'm not sure I like the name pci_p2p_same_segment. It reads as though
>> it's only checking if the devices are not the same segment.
> 
> Well, that is exactly what it is doing. If it succeeds then the caller
> knows the DMA will not flow outside the segment and no iommu setup/etc
> is required.

It appears to me like it's calculating the DMA address, and the check is
just a side requirement. It reads as though it's only doing the check.

Logan

  reply	other threads:[~2017-04-19 19:02 UTC|newest]

Thread overview: 105+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-16 15:44 [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Dan Williams
2017-04-16 16:47 ` Logan Gunthorpe
2017-04-16 22:32   ` Benjamin Herrenschmidt
2017-04-17  5:13     ` Logan Gunthorpe
2017-04-17  7:20       ` Benjamin Herrenschmidt
2017-04-17 16:52         ` Logan Gunthorpe
2017-04-17 17:04           ` Dan Williams
2017-04-18  5:22             ` Logan Gunthorpe
2017-04-17 18:04           ` Jerome Glisse
2017-04-18  6:14             ` Logan Gunthorpe
2017-04-17 21:11           ` Benjamin Herrenschmidt
2017-04-18  5:43             ` Logan Gunthorpe
2017-04-18  6:29               ` Benjamin Herrenschmidt
2017-04-16 22:23 ` Benjamin Herrenschmidt
2017-04-18 16:45   ` Jason Gunthorpe
2017-04-18 17:27     ` Dan Williams
2017-04-18 18:00       ` Jason Gunthorpe
2017-04-18 18:34         ` Dan Williams
2017-04-19  1:13         ` Benjamin Herrenschmidt
2017-04-18 22:46       ` Benjamin Herrenschmidt
2017-04-18 22:52         ` Dan Williams
2017-04-18 18:30     ` Logan Gunthorpe
2017-04-18 19:01       ` Jason Gunthorpe
2017-04-18 19:35         ` Logan Gunthorpe
2017-04-18 19:48           ` Dan Williams
2017-04-18 20:29             ` Jerome Glisse
2017-04-18 20:31               ` Dan Williams
2017-04-18 20:48                 ` Logan Gunthorpe
2017-04-19  1:17                   ` Benjamin Herrenschmidt
2017-04-18 21:03             ` Jason Gunthorpe
2017-04-18 21:11               ` Dan Williams
2017-04-18 21:22                 ` Jason Gunthorpe
2017-04-18 21:36                   ` Dan Williams
2017-04-18 22:15                     ` Logan Gunthorpe
2017-04-18 22:28                       ` Dan Williams
2017-04-18 22:42                         ` Jason Gunthorpe
2017-04-18 22:51                           ` Dan Williams
2017-04-18 23:21                             ` Jason Gunthorpe
2017-04-19  1:25                               ` Benjamin Herrenschmidt
2017-04-18 22:48                         ` Logan Gunthorpe
2017-04-18 22:50                           ` Dan Williams
2017-04-18 22:56                             ` Logan Gunthorpe
2017-04-18 23:02                               ` Dan Williams
2017-04-19  1:21                   ` Benjamin Herrenschmidt
2017-04-18 21:31               ` Logan Gunthorpe
2017-04-18 22:24                 ` Jason Gunthorpe
2017-04-18 23:03                   ` Logan Gunthorpe
2017-04-19  1:23                   ` Benjamin Herrenschmidt
2017-04-19  1:20               ` Benjamin Herrenschmidt
2017-04-19 15:55                 ` Jason Gunthorpe
2017-04-19 16:48                   ` Logan Gunthorpe
2017-04-19 17:01                     ` Dan Williams
2017-04-19 17:32                       ` Jerome Glisse
2017-04-19 17:41                         ` Dan Williams
2017-04-19 18:11                           ` Logan Gunthorpe
2017-04-19 18:19                             ` Logan Gunthorpe
2017-04-19 18:30                               ` Dan Williams
2017-04-19 18:41                                 ` Logan Gunthorpe
2017-04-19 18:44                                   ` Dan Williams
2017-04-20 20:43                           ` Stephen  Bates
2017-04-20 20:47                             ` Dan Williams
2017-04-20 23:07                               ` Stephen  Bates
2017-04-21  4:59                                 ` Dan Williams
2017-04-19 17:14                     ` Jason Gunthorpe
2017-04-19 18:01                       ` Logan Gunthorpe
2017-04-19 18:32                         ` Jason Gunthorpe
2017-04-19 19:02                           ` Logan Gunthorpe [this message]
2017-04-19 19:31                             ` Jason Gunthorpe
2017-04-19 19:41                               ` Logan Gunthorpe
2017-04-19 20:48                                 ` Jason Gunthorpe
2017-04-19 22:55                                   ` Logan Gunthorpe
2017-04-20  0:07                                     ` Dan Williams
2017-04-18 19:48           ` Jason Gunthorpe
2017-04-18 20:06             ` Logan Gunthorpe
  -- strict thread matches above, loose matches on Subject: below --
2017-03-30 22:12 Logan Gunthorpe
2017-04-12  5:22 ` Benjamin Herrenschmidt
2017-04-12 17:09   ` Logan Gunthorpe
2017-04-12 21:55     ` Benjamin Herrenschmidt
2017-04-13 21:22       ` Logan Gunthorpe
2017-04-13 22:37         ` Benjamin Herrenschmidt
2017-04-13 23:26         ` Bjorn Helgaas
2017-04-14  4:16           ` Jason Gunthorpe
2017-04-14  4:40             ` Logan Gunthorpe
2017-04-14 11:37               ` Benjamin Herrenschmidt
2017-04-14 11:39                 ` Benjamin Herrenschmidt
2017-04-14 11:37             ` Benjamin Herrenschmidt
2017-04-14 17:30               ` Logan Gunthorpe
2017-04-14 19:04                 ` Bjorn Helgaas
2017-04-14 22:07                   ` Benjamin Herrenschmidt
2017-04-15 17:41                     ` Logan Gunthorpe
2017-04-15 22:09                       ` Dan Williams
2017-04-16  3:01                         ` Benjamin Herrenschmidt
2017-04-16  4:46                           ` Logan Gunthorpe
2017-04-16 15:53                           ` Dan Williams
2017-04-16 16:34                             ` Logan Gunthorpe
2017-04-16 22:31                               ` Benjamin Herrenschmidt
2017-04-24  7:36                                 ` Knut Omang
2017-04-24 16:14                                   ` Logan Gunthorpe
2017-04-25  6:30                                     ` Knut Omang
2017-04-25 17:03                                       ` Logan Gunthorpe
2017-04-25 21:23                                         ` Stephen  Bates
2017-04-25 21:23                                   ` Stephen  Bates
2017-04-16 22:26                             ` Benjamin Herrenschmidt
2017-04-15 22:17                       ` Benjamin Herrenschmidt
2017-04-16  5:36                         ` Logan Gunthorpe

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