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From: Robin Murphy <robin.murphy@arm.com>
To: Yongji Xie <xieyongji@bytedance.com>, Jason Wang <jasowang@redhat.com>
Cc: kvm <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>,
	virtualization <virtualization@lists.linux-foundation.org>,
	"Christian Brauner" <christian.brauner@canonical.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Carpenter" <dan.carpenter@oracle.com>,
	"Stefano Garzarella" <sgarzare@redhat.com>,
	"Liu Xiaodong" <xiaodong.liu@intel.com>,
	linux-fsdevel@vger.kernel.org,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	songmuchun@bytedance.com, "Jens Axboe" <axboe@kernel.dk>,
	"He Zhe" <zhe.he@windriver.com>,
	"Greg KH" <gregkh@linuxfoundation.org>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	iommu@lists.linux-foundation.org, bcrl@kvack.org,
	netdev@vger.kernel.org, "Joe Perches" <joe@perches.com>,
	"Mika Penttilä" <mika.penttila@nextfour.com>
Subject: Re: [PATCH v10 01/17] iova: Export alloc_iova_fast() and free_iova_fast()
Date: Tue, 3 Aug 2021 11:53:45 +0100	[thread overview]
Message-ID: <6e05e25e-e569-402e-d81b-8ac2cff1c0e8@arm.com> (raw)
In-Reply-To: <CACycT3vcpwyA3xjD29f1hGnYALyAd=-XcWp8+wJiwSqpqUu00w@mail.gmail.com>

On 2021-08-03 09:54, Yongji Xie wrote:
> On Tue, Aug 3, 2021 at 3:41 PM Jason Wang <jasowang@redhat.com> wrote:
>>
>>
>> 在 2021/7/29 下午3:34, Xie Yongji 写道:
>>> Export alloc_iova_fast() and free_iova_fast() so that
>>> some modules can use it to improve iova allocation efficiency.
>>
>>
>> It's better to explain why alloc_iova() is not sufficient here.
>>
> 
> Fine.

What I fail to understand from the later patches is what the IOVA domain 
actually represents. If the "device" is a userspace process then 
logically the "IOVA" would be the userspace address, so presumably 
somewhere you're having to translate between this arbitrary address 
space and actual usable addresses - if you're worried about efficiency 
surely it would be even better to not do that?

Presumably userspace doesn't have any concern about alignment and the 
things we have to worry about for the DMA API in general, so it's pretty 
much just allocating slots in a buffer, and there are far more effective 
ways to do that than a full-blown address space manager. If you're going 
to reuse any infrastructure I'd have expected it to be SWIOTLB rather 
than the IOVA allocator. Because, y'know, you're *literally implementing 
a software I/O TLB* ;)

Robin.

  reply	other threads:[~2021-08-03 10:54 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-29  7:34 [PATCH v10 00/17] Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-07-29  7:34 ` [PATCH v10 01/17] iova: Export alloc_iova_fast() and free_iova_fast() Xie Yongji
2021-08-03  7:41   ` Jason Wang
2021-08-03  7:41   ` Jason Wang
2021-08-03  8:54     ` Yongji Xie
2021-08-03 10:53       ` Robin Murphy [this message]
2021-08-04  5:02         ` Yongji Xie
2021-08-04 15:43           ` Robin Murphy
2021-08-05 12:34             ` Yongji Xie
2021-08-05 13:31               ` Jason Wang
2021-08-09  5:56                 ` Yongji Xie
2021-08-10  3:02                   ` Jason Wang
2021-08-10  7:43                     ` Yongji Xie
2021-07-29  7:34 ` [PATCH v10 02/17] file: Export receive_fd() to modules Xie Yongji
2021-08-03  7:45   ` Jason Wang
2021-08-03  9:01     ` Yongji Xie
2021-08-04  8:27       ` Jason Wang
2021-07-29  7:34 ` [PATCH v10 03/17] vdpa: Fix code indentation Xie Yongji
2021-08-03  7:50   ` Jason Wang
2021-08-03  9:13     ` Yongji Xie
2021-07-29  7:34 ` [PATCH v10 04/17] vdpa: Fail the vdpa_reset() if fail to set device status to zero Xie Yongji
2021-08-03  7:58   ` Jason Wang
2021-08-03  9:31     ` Yongji Xie
2021-08-04  8:30       ` Jason Wang
2021-07-29  7:34 ` [PATCH v10 05/17] vhost-vdpa: Fail the vhost_vdpa_set_status() on reset failure Xie Yongji
2021-08-03  8:10   ` Jason Wang
2021-08-03  9:50     ` Yongji Xie
2021-08-04  8:33       ` Jason Wang
2021-07-29  7:34 ` [PATCH v10 06/17] vhost-vdpa: Handle the failure of vdpa_reset() Xie Yongji
2021-07-29  7:34 ` [PATCH v10 07/17] virtio: Don't set FAILED status bit on device index allocation failure Xie Yongji
2021-08-03  8:02   ` Jason Wang
2021-08-03  9:17     ` Yongji Xie
2021-07-29  7:34 ` [PATCH v10 08/17] virtio_config: Add a return value to reset function Xie Yongji
2021-07-29  7:34 ` [PATCH v10 09/17] virtio-vdpa: Handle the failure of vdpa_reset() Xie Yongji
2021-07-29  7:34 ` [PATCH v10 10/17] virtio: Handle device reset failure in register_virtio_device() Xie Yongji
2021-08-03  8:09   ` Jason Wang
2021-08-03  9:38     ` Yongji Xie
2021-08-04  8:32       ` Jason Wang
2021-08-04  8:50         ` Yongji Xie
2021-08-04  8:54           ` Jason Wang
2021-08-04  9:07             ` Yongji Xie
2021-08-05  7:12               ` Jason Wang
2021-07-29  7:34 ` [PATCH v10 11/17] vhost-iotlb: Add an opaque pointer for vhost IOTLB Xie Yongji
2021-07-29  7:34 ` [PATCH v10 12/17] vdpa: Add an opaque pointer for vdpa_config_ops.dma_map() Xie Yongji
2021-07-29  7:34 ` [PATCH v10 13/17] vdpa: factor out vhost_vdpa_pa_map() and vhost_vdpa_pa_unmap() Xie Yongji
2021-07-29  7:35 ` [PATCH v10 14/17] vdpa: Support transferring virtual addressing during DMA mapping Xie Yongji
2021-07-29  7:35 ` [PATCH v10 15/17] vduse: Implement an MMU-based software IOTLB Xie Yongji
2021-07-29  7:35 ` [PATCH v10 16/17] vduse: Introduce VDUSE - vDPA Device in Userspace Xie Yongji
2021-07-29  9:00   ` Greg KH
2021-07-29  9:57     ` Yongji Xie
2021-08-03  7:30   ` Jason Wang
2021-08-03  8:39     ` Yongji Xie
2021-07-29  7:35 ` [PATCH v10 17/17] Documentation: Add documentation for VDUSE Xie Yongji
2021-08-03  7:35   ` Jason Wang
2021-08-03  8:52     ` Yongji Xie

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