From: Dan Williams <dan.j.williams@intel.com>
To: Logan Gunthorpe <logang@deltatee.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Bjorn Helgaas <helgaas@kernel.org>,
Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
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: Sat, 15 Apr 2017 15:09:08 -0700 [thread overview]
Message-ID: <CAPcyv4jUeKzKDARp6Z35kdPLKnP-M6aF8X5KpOx55CLyjnj4dA@mail.gmail.com> (raw)
In-Reply-To: <bff1e503-95a9-e19f-bfd9-0ff962c63a81@deltatee.com>
On Sat, Apr 15, 2017 at 10:41 AM, Logan Gunthorpe <logang@deltatee.com> wrote:
> Thanks, Benjamin, for the summary of some of the issues.
>
> On 14/04/17 04:07 PM, Benjamin Herrenschmidt wrote
>> So I assume the p2p code provides a way to address that too via special
>> dma_ops ? Or wrappers ?
>
> Not at this time. We will probably need a way to ensure the iommus do
> not attempt to remap these addresses. Though if it does, I'd expect
> everything would still work you just wouldn't get the performance or
> traffic flow you are looking for. We've been testing with the software
> iommu which doesn't have this problem.
>
>> The problem is that the latter while seemingly easier, is also slower
>> and not supported by all platforms and architectures (for example,
>> POWER currently won't allow it, or rather only allows a store-only
>> subset of it under special circumstances).
>
> Yes, I think situations where we have to cross host bridges will remain
> unsupported by this work for a long time. There are two many cases where
> it just doesn't work or it performs too poorly to be useful.
>
>> I don't fully understand how p2pmem "solves" that by creating struct
>> pages. The offset problem is one issue. But there's the iommu issue as
>> well, the driver cannot just use the normal dma_map ops.
>
> We are not using a proper iommu and we are dealing with systems that
> have zero offset. This case is also easily supported. I expect fixing
> the iommus to not map these addresses would also be reasonably achievable.
I'm wondering, since this is limited to support behind a single
switch, if you could have a software-iommu hanging off that switch
device object that knows how to catch and translate the non-zero
offset bus address case. We have something like this with VMD driver,
and I toyed with a soft pci bridge when trying to support AHCI+NVME
bar remapping. When the dma api looks up the iommu for its device it
hits this soft-iommu and that driver checks if the page is host memory
or device memory to do the dma translation. You wouldn't need a bit in
struct page, just a lookup to the hosting struct dev_pagemap in the
is_zone_device_page() case and that can point you to p2p details.
next prev parent reply other threads:[~2017-04-15 22:09 UTC|newest]
Thread overview: 155+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-30 22:12 [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory Logan Gunthorpe
2017-03-30 22:12 ` [RFC 1/8] Introduce Peer-to-Peer memory (p2pmem) device Logan Gunthorpe
2017-03-31 18:49 ` Sinan Kaya
2017-03-31 21:23 ` Logan Gunthorpe
2017-03-31 21:38 ` Sinan Kaya
2017-03-31 22:42 ` Logan Gunthorpe
2017-03-31 23:51 ` Sinan Kaya
2017-04-01 1:57 ` Logan Gunthorpe
2017-04-01 2:17 ` okaya
2017-04-01 22:16 ` Logan Gunthorpe
2017-04-02 2:26 ` Sinan Kaya
2017-04-02 17:21 ` Logan Gunthorpe
2017-04-02 21:03 ` Sinan Kaya
2017-04-03 4:26 ` Logan Gunthorpe
2017-04-25 11:58 ` Marta Rybczynska
2017-04-25 16:58 ` Logan Gunthorpe
2017-03-30 22:12 ` [RFC 2/8] cxgb4: setup pcie memory window 4 and create p2pmem region Logan Gunthorpe
2017-04-04 10:42 ` Sagi Grimberg
2017-04-04 15:56 ` Logan Gunthorpe
2017-04-05 15:41 ` Steve Wise
2017-03-30 22:12 ` [RFC 3/8] nvmet: Use p2pmem in nvme target Logan Gunthorpe
2017-04-04 10:40 ` Sagi Grimberg
2017-04-04 16:16 ` Logan Gunthorpe
2017-04-06 5:47 ` Sagi Grimberg
2017-04-06 15:52 ` Logan Gunthorpe
2017-03-30 22:12 ` [RFC 4/8] p2pmem: Add debugfs "stats" file Logan Gunthorpe
2017-04-04 10:46 ` Sagi Grimberg
2017-04-04 17:25 ` Logan Gunthorpe
2017-04-05 15:43 ` Steve Wise
2017-03-30 22:12 ` [RFC 5/8] scatterlist: Modify SG copy functions to support io memory Logan Gunthorpe
2017-03-31 7:09 ` Christoph Hellwig
2017-03-31 15:41 ` Logan Gunthorpe
2017-04-03 21:20 ` Logan Gunthorpe
2017-04-03 21:44 ` Dan Williams
2017-04-03 22:10 ` Logan Gunthorpe
2017-04-03 22:47 ` Dan Williams
2017-04-03 23:12 ` Logan Gunthorpe
2017-04-04 0:07 ` Dan Williams
2017-04-07 17:59 ` Logan Gunthorpe
2017-03-30 22:12 ` [RFC 6/8] nvmet: Be careful about using iomem accesses when dealing with p2pmem Logan Gunthorpe
2017-04-04 10:59 ` Sagi Grimberg
2017-04-04 15:46 ` Jason Gunthorpe
2017-04-04 17:21 ` Logan Gunthorpe
2017-04-06 5:33 ` Sagi Grimberg
2017-04-06 16:02 ` Logan Gunthorpe
2017-04-06 16:35 ` Jason Gunthorpe
2017-04-07 11:19 ` Stephen Bates
2017-04-10 8:29 ` Sagi Grimberg
2017-04-10 16:03 ` Logan Gunthorpe
2017-03-30 22:12 ` [RFC 7/8] p2pmem: Support device removal Logan Gunthorpe
2017-03-30 22:12 ` [RFC 8/8] p2pmem: Added char device user interface Logan Gunthorpe
2017-04-12 5:22 ` [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory 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 [this message]
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
2017-04-16 15:44 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
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
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