From: Jason Wang <jasowang@redhat.com>
To: "Tian, Kevin" <kevin.tian@intel.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Alex Williamson <alex.williamson@redhat.com>
Cc: "Jiang, Dave" <dave.jiang@intel.com>,
"vkoul@kernel.org" <vkoul@kernel.org>,
"Dey, Megha" <megha.dey@intel.com>,
"maz@kernel.org" <maz@kernel.org>,
"bhelgaas@google.com" <bhelgaas@google.com>,
"rafael@kernel.org" <rafael@kernel.org>,
"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"hpa@zytor.com" <hpa@zytor.com>,
"Pan, Jacob jun" <jacob.jun.pan@intel.com>,
"Raj, Ashok" <ashok.raj@intel.com>,
"Liu, Yi L" <yi.l.liu@intel.com>,
"Lu, Baolu" <baolu.lu@intel.com>,
"Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
"Luck, Tony" <tony.luck@intel.com>,
"Lin, Jing" <jing.lin@intel.com>,
"Williams, Dan J" <dan.j.williams@intel.com>,
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"Hansen, Dave" <dave.hansen@intel.com>,
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"Hossain, Mona" <mona.hossain@intel.com>,
"dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI support for the idxd driver
Date: Thu, 13 Aug 2020 14:01:58 +0800 [thread overview]
Message-ID: <e3f45862-c3a5-8bac-e04d-7be0e76908a9@redhat.com> (raw)
In-Reply-To: <MWHPR11MB1645F911EFB993C9067B58DD8C430@MWHPR11MB1645.namprd11.prod.outlook.com>
On 2020/8/13 下午1:26, Tian, Kevin wrote:
>> From: Jason Wang <jasowang@redhat.com>
>> Sent: Thursday, August 13, 2020 12:34 PM
>>
>>
>> On 2020/8/12 下午12:05, Tian, Kevin wrote:
>>>> The problem is that if we tie all controls via VFIO uAPI, the other
>>>> subsystem like vDPA is likely to duplicate them. I wonder if there is a
>>>> way to decouple the vSVA out of VFIO uAPI?
>>> vSVA is a per-device (either pdev or mdev) feature thus naturally should
>>> be managed by its device driver (VFIO or vDPA). From this angle some
>>> duplication is inevitable given VFIO and vDPA are orthogonal passthrough
>>> frameworks. Within the kernel the majority of vSVA handling is done by
>>> IOMMU and IOASID modules thus most logic are shared.
>>
>> So why not introduce vSVA uAPI at IOMMU or IOASID layer?
> One may ask a similar question why IOMMU doesn't expose map/unmap
> as uAPI...
I think this is probably a good idea as well. If there's anything missed
in the infrastructure, we can invent. Besides vhost-vDPA, there are
other subsystems that relaying their uAPI to IOMMU API. Duplicating
uAPIs is usually a hint of the codes duplication. Simple map/unmap could
be easy but vSVA uAPI is much more complicated.
>
>>
>>>>> If an userspace DMA interface can be easily
>>>>> adapted to be a passthrough one, it might be the choice.
>>>> It's not that easy even for VFIO which requires a lot of new uAPIs and
>>>> infrastructures(e.g mdev) to be invented.
>>>>
>>>>
>>>>> But for idxd,
>>>>> we see mdev a much better fit here, given the big difference between
>>>>> what userspace DMA requires and what guest driver requires in this hw.
>>>> A weak point for mdev is that it can't serve kernel subsystem other than
>>>> VFIO. In this case, you need some other infrastructures (like [1]) to do
>>>> this.
>>> mdev is not exclusive from kernel usages. It's perfectly fine for a driver
>>> to reserve some work queues for host usages, while wrapping others
>>> into mdevs.
>>
>> I meant you may want slices to be an independent device from the kernel
>> point of view:
>>
>> E.g for ethernet devices, you may want 10K mdevs to be passed to guest.
>>
>> Similarly, you may want 10K net devices which is connected to the kernel
>> networking subsystems.
>>
>> In this case it's not simply reserving queues but you need some other
>> type of device abstraction. There could be some kind of duplication
>> between this and mdev.
>>
> yes, some abstraction required but isn't it what the driver should
> care about instead of mdev framework itself?
With mdev you present a "PCI" device, but what's kind of device it tries
to present to kernel? If it's still PCI, there's duplication with mdev,
if it's something new, maybe we can switch to that API.
> If the driver reports
> the same set of resource to both mdev and networking, it needs to
> make sure when the resource is claimed in one interface then it
> should be marked in-use in another. e.g. each mdev includes a
> available_intances attribute. the driver could report 10k available
> instances initially and then update it to 5K when another 5K is used
> for net devices later.
Right but this probably means you need another management layer under mdev.
>
> Mdev definitely has its usage limitations. Some may be improved
> in the future, some may not. But those are distracting from the
> original purpose of this thread (mdev vs. userspace DMA) and better
> be discussed in other places e.g. LPC...
Ok.
Thanks
>
> Thanks
> Kevin
next prev parent reply other threads:[~2020-08-13 6:02 UTC|newest]
Thread overview: 97+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 16:02 [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI support for the idxd driver Dave Jiang
2020-07-21 16:02 ` [PATCH RFC v2 01/18] platform-msi: Introduce platform_msi_ops Dave Jiang
2020-07-21 16:02 ` [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI irq domain Dave Jiang
2020-07-21 16:13 ` Jason Gunthorpe
2020-07-22 16:50 ` Dey, Megha
2020-07-22 18:52 ` Marc Zyngier
2020-07-22 19:59 ` Jason Gunthorpe
2020-07-23 8:51 ` Marc Zyngier
2020-07-24 0:16 ` Jason Gunthorpe
2020-07-24 0:36 ` Thomas Gleixner
2020-08-05 19:18 ` Dey, Megha
2020-08-05 22:15 ` Jason Gunthorpe
2020-08-05 22:36 ` Dey, Megha
2020-08-05 22:53 ` Jason Gunthorpe
2020-08-06 0:13 ` Dey, Megha
2020-08-06 0:19 ` Jason Gunthorpe
2020-08-06 0:32 ` Dey, Megha
2020-08-06 0:46 ` Jason Gunthorpe
2020-08-06 17:10 ` Thomas Gleixner
2020-08-06 17:58 ` Dey, Megha
2020-08-06 20:21 ` Thomas Gleixner
2020-08-06 22:27 ` Dey, Megha
2020-08-07 8:48 ` Thomas Gleixner
2020-08-07 12:06 ` Jason Gunthorpe
2020-08-07 12:38 ` gregkh
2020-08-07 13:34 ` Jason Gunthorpe
2020-08-07 16:47 ` Thomas Gleixner
2020-08-07 17:54 ` Dey, Megha
2020-08-07 18:39 ` Jason Gunthorpe
2020-08-07 20:31 ` Dey, Megha
2020-08-08 19:47 ` Thomas Gleixner
2020-08-10 21:46 ` Thomas Gleixner
2020-08-11 9:53 ` Thomas Gleixner
2020-08-11 18:46 ` Dey, Megha
2020-08-11 21:25 ` Thomas Gleixner
2020-08-11 18:39 ` Dey, Megha
2020-08-11 22:39 ` Thomas Gleixner
2020-08-07 15:22 ` Thomas Gleixner
2020-08-05 18:55 ` Dey, Megha
2020-07-21 16:02 ` [PATCH RFC v2 03/18] irq/dev-msi: Create IR-DEV-MSI " Dave Jiang
2020-07-21 16:21 ` Jason Gunthorpe
2020-07-22 17:03 ` Dey, Megha
2020-07-22 17:33 ` Jason Gunthorpe
2020-07-22 20:44 ` Thomas Gleixner
2020-08-05 19:02 ` Dey, Megha
2020-07-21 16:02 ` [PATCH RFC v2 04/18] irq/dev-msi: Introduce APIs to allocate/free dev-msi interrupts Dave Jiang
2020-07-21 16:25 ` Jason Gunthorpe
2020-07-22 17:05 ` Dey, Megha
2020-07-22 17:35 ` Jason Gunthorpe
2020-08-05 20:19 ` Dey, Megha
2020-07-21 16:02 ` [PATCH RFC v2 05/18] dmaengine: idxd: add support for readonly config devices Dave Jiang
2020-07-21 16:02 ` [PATCH RFC v2 06/18] dmaengine: idxd: add interrupt handle request support Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 07/18] dmaengine: idxd: add DEV-MSI support in base driver Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 08/18] dmaengine: idxd: add device support functions in prep for mdev Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 09/18] dmaengine: idxd: add basic mdev registration and helper functions Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 10/18] dmaengine: idxd: add emulation rw routines Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 11/18] dmaengine: idxd: prep for virtual device commands Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 12/18] dmaengine: idxd: virtual device commands emulation Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 13/18] dmaengine: idxd: ims setup for the vdcm Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 14/18] dmaengine: idxd: add mdev type as a new wq type Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 15/18] dmaengine: idxd: add dedicated wq mdev type Dave Jiang
2020-07-21 16:04 ` [PATCH RFC v2 16/18] dmaengine: idxd: add new wq state for mdev Dave Jiang
2020-07-21 16:04 ` [PATCH RFC v2 17/18] dmaengine: idxd: add error notification from host driver to mediated device Dave Jiang
2020-07-21 16:04 ` [PATCH RFC v2 18/18] dmaengine: idxd: add ABI documentation for mediated device support Dave Jiang
2020-07-21 16:28 ` [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI support for the idxd driver Greg KH
2020-07-21 17:17 ` Dave Jiang
2020-07-21 21:35 ` Dan Williams
2020-07-21 16:45 ` Jason Gunthorpe
2020-07-21 18:00 ` Dave Jiang
2020-07-22 17:31 ` Dey, Megha
2020-07-22 18:16 ` Jason Gunthorpe
2020-07-21 23:54 ` Tian, Kevin
2020-07-24 0:19 ` Jason Gunthorpe
2020-08-06 1:22 ` Alex Williamson
2020-08-07 12:19 ` Jason Gunthorpe
2020-08-10 7:32 ` Tian, Kevin
2020-08-11 17:00 ` Alex Williamson
2020-08-12 1:58 ` Tian, Kevin
2020-08-12 2:36 ` Alex Williamson
2020-08-12 3:35 ` Tian, Kevin
2020-08-12 3:28 ` Jason Wang
2020-08-12 4:05 ` Tian, Kevin
2020-08-13 4:33 ` Jason Wang
2020-08-13 5:26 ` Tian, Kevin
2020-08-13 6:01 ` Jason Wang [this message]
2020-08-14 13:23 ` Jason Gunthorpe
2020-08-17 2:24 ` Tian, Kevin
2020-08-14 13:35 ` Jason Gunthorpe
2020-08-17 2:12 ` Tian, Kevin
2020-08-18 0:43 ` Jason Gunthorpe
2020-08-18 1:09 ` Tian, Kevin
2020-08-18 11:50 ` Jason Gunthorpe
2020-08-18 16:27 ` Paolo Bonzini
2020-08-18 16:49 ` Jason Gunthorpe
2020-08-18 17:05 ` Paolo Bonzini
2020-08-18 17:18 ` Jason Gunthorpe
2020-08-19 7:29 ` Tian, Kevin
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