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From: "Dey, Megha" <megha.dey@linux.intel.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: Dave Jiang <dave.jiang@intel.com>,
	vkoul@kernel.org, maz@kernel.org, bhelgaas@google.com,
	rafael@kernel.org, gregkh@linuxfoundation.org,
	tglx@linutronix.de, hpa@zytor.com, alex.williamson@redhat.com,
	jacob.jun.pan@intel.com, ashok.raj@intel.com, yi.l.liu@intel.com,
	baolu.lu@intel.com, kevin.tian@intel.com,
	sanjay.k.kumar@intel.com, tony.luck@intel.com,
	jing.lin@intel.com, dan.j.williams@intel.com,
	kwankhede@nvidia.com, eric.auger@redhat.com, parav@mellanox.com,
	dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver.
Date: Fri, 1 May 2020 15:32:35 -0700	[thread overview]
Message-ID: <30dadd7a-bac2-d658-c2e4-77592de6118d@linux.intel.com> (raw)
In-Reply-To: <20200423194447.GF13640@mellanox.com>



On 4/23/2020 12:44 PM, Jason Gunthorpe wrote:
>>>> The mdev utilizes Interrupt Message Store or IMS[3] instead of MSIX for
>>>> interrupts for the guest. This preserves MSIX for host usages and also allows a
>>>> significantly larger number of interrupt vectors for guest usage.
>>>
>>> I never did get a reply to my earlier remarks on the IMS patches.
>>>
>>> The concept of a device specific addr/data table format for MSI is not
>>> Intel specific. This should be general code. We have a device that can
>>> use this kind of kernel capability today.
>>
>> I am sorry if I did not address your comments earlier.
> 
> It appears noboy from Intel bothered to answer anyone else on that RFC
> thread:
> 
> https://lore.kernel.org/lkml/1568338328-22458-1-git-send-email-megha.dey@linux.intel.com/
> 
> However, it seems kind of moot as I see now that this verion of IMS
> bears almost no resemblance to the original RFC.

hmm yeah, we changed most of the code after getting a lot of feedback 
from you and folks at plumbers. But yes, I should have replied to all 
the feedback, lesson learnt :)

> 
> That said, the similiarity to platform-msi was striking, does this new
> version harmonize with that?

yes!
> 
>> The present IMS code is quite generic, most of the code is in the drivers/
>> folder. We basically introduce 2 APIS: allocate and free IMS interrupts and
>> a IMS IRQ domain to allocate these interrupts from. These APIs are
>> architecture agnostic.
>>
>> We also introduce a new IMS IRQ domain which is architecture specific. This
>> is because IMS generates interrupts only in the remappable format, hence
>> interrupt remapping should be enabled for IMS. Currently, the interrupt
>> remapping code is only available for Intel and AMD and I don’t see anything
>> for ARM.
> 
> I don't understand these remarks though - IMS is simply the mapping of
> a MemWr addr/data pair to a Linux IRQ number? Why does this intersect
> with remapping?
> 

 From your comments so far, I think your requirement is a subset of what 
IMS is trying to do.

What you want:
have a dynamic means of allocating platform-msi interrupts

On top of this IMS has a requirement that all of the interrupts should 
be remapped.

So we can have tiered code: generic dynamic platform-msi infrastructure
and add the IMS specific bits (Intel specific) on top of this.

The generic code will have no reference to IMS.

> AFAIK, any platform that supports MSI today should have the inherent
> HW capability to support IMS.
> 
>> Also, could you give more details on the device that could use IMS? Do you
>> have some driver code already? We could then see if and how the current IMS
>> code could be made more generic.
> 
> We have several devices of interest, our NICs have very flexible PCI,
> so it is no problem to take the MemWR addr/data from someplace other
> than the MSI tables.
> 
> For this we want to have some way to allocate Linux IRQs dynamically
> and get a addr/data pair to trigger them.
> 
> Our NIC devices are also linked to our ARM SOC family, so I'd expect
> our ARM's to also be able to provide these APIs as the platform.

cool, so I will hope that you can test out the generic APIs from the ARM 
side!
> 
> Jason
> 

  reply	other threads:[~2020-05-01 22:32 UTC|newest]

Thread overview: 89+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21 23:33 Dave Jiang
2020-04-21 23:33 ` [PATCH RFC 01/15] drivers/base: Introduce platform_msi_ops Dave Jiang
2020-04-26  7:01   ` Greg KH
2020-04-27 21:38     ` Dave Jiang
2020-04-28  7:34       ` Greg KH
2020-04-21 23:33 ` [PATCH RFC 02/15] drivers/base: Introduce a new platform-msi list Dave Jiang
2020-04-25 21:13   ` Thomas Gleixner
2020-05-04  0:08     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 03/15] drivers/base: Allocate/free platform-msi interrupts by group Dave Jiang
2020-04-25 21:23   ` Thomas Gleixner
2020-05-04  0:08     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 04/15] drivers/base: Add support for a new IMS irq domain Dave Jiang
2020-04-23 20:11   ` Jason Gunthorpe
2020-05-01 22:30     ` Dey, Megha
2020-05-03 22:25       ` Jason Gunthorpe
2020-05-03 22:40         ` Dey, Megha
2020-05-03 22:46           ` Jason Gunthorpe
2020-05-04  0:25             ` Dey, Megha
2020-05-04 12:14               ` Jason Gunthorpe
2020-05-06 10:27                 ` Tian, Kevin
2020-04-25 21:38   ` Thomas Gleixner
2020-05-04  0:11     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 05/15] ims-msi: Add mask/unmask routines Dave Jiang
2020-04-25 21:49   ` Thomas Gleixner
2020-05-04  0:16     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 06/15] ims-msi: Enable IMS interrupts Dave Jiang
2020-04-25 22:13   ` Thomas Gleixner
2020-05-04  0:17     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 07/15] Documentation: Interrupt Message store Dave Jiang
2020-04-23 20:04   ` Jason Gunthorpe
2020-05-01 22:32     ` Dey, Megha
2020-05-03 22:28       ` Jason Gunthorpe
2020-05-03 22:41         ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 08/15] vfio/mdev: Add a member for iommu domain in mdev_device Dave Jiang
2020-04-21 23:34 ` [PATCH RFC 09/15] vfio/type1: Save domain when attach domain to mdev Dave Jiang
2020-04-21 23:34 ` [PATCH RFC 10/15] dmaengine: idxd: add config support for readonly devices Dave Jiang
2020-04-21 23:34 ` [PATCH RFC 11/15] dmaengine: idxd: add IMS support in base driver Dave Jiang
2020-04-21 23:35 ` [PATCH RFC 12/15] dmaengine: idxd: add device support functions in prep for mdev Dave Jiang
2020-04-21 23:35 ` [PATCH RFC 13/15] dmaengine: idxd: add support for VFIO mediated device Dave Jiang
2020-04-21 23:35 ` [PATCH RFC 14/15] dmaengine: idxd: add error notification from host driver to " Dave Jiang
2020-04-21 23:35 ` [PATCH RFC 15/15] dmaengine: idxd: add ABI documentation for mediated device support Dave Jiang
2020-04-21 23:54 ` [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver Jason Gunthorpe
2020-04-22  0:53   ` Tian, Kevin
2020-04-22 11:50     ` Jason Gunthorpe
2020-04-22 21:14       ` Raj, Ashok
2020-04-23 19:12         ` Jason Gunthorpe
2020-04-24  3:27           ` Tian, Kevin
2020-04-24 12:44             ` Jason Gunthorpe
2020-04-24 16:25               ` Tian, Kevin
2020-04-24 18:12                 ` Jason Gunthorpe
2020-04-26  5:18                   ` Tian, Kevin
2020-04-26 19:13                     ` Jason Gunthorpe
2020-04-27  3:43                       ` Alex Williamson
2020-04-27 11:58                         ` Jason Gunthorpe
2020-04-27 13:19                           ` Alex Williamson
2020-04-27 13:22                             ` Jason Gunthorpe
2020-04-27 14:18                               ` Alex Williamson
2020-04-27 14:25                                 ` Jason Gunthorpe
2020-04-27 15:41                                   ` Alex Williamson
2020-04-27 16:16                                     ` Jason Gunthorpe
2020-04-27 16:25                                       ` Dave Jiang
2020-04-27 21:56                                         ` Jason Gunthorpe
2020-04-29  9:42                               ` Tian, Kevin
2020-05-08 20:47                                 ` Raj, Ashok
2020-05-08 23:16                                   ` Jason Gunthorpe
2020-05-08 23:52                                     ` Dave Jiang
2020-05-09  0:09                                     ` Raj, Ashok
2020-05-09 12:21                                       ` Jason Gunthorpe
2020-05-13  2:29                                         ` Jason Wang
2020-05-13  8:30                                         ` Tian, Kevin
2020-05-13 12:40                                           ` Jason Gunthorpe
2020-04-27 12:13                       ` Tian, Kevin
2020-04-27 12:55                         ` Jason Gunthorpe
2020-04-22 21:24   ` Dan Williams
2020-04-23 19:17     ` Dan Williams
2020-04-23 19:49       ` Jason Gunthorpe
2020-05-01 22:31         ` Dey, Megha
2020-05-03 22:21           ` Jason Gunthorpe
2020-05-03 22:32             ` Dey, Megha
2020-04-23 19:18     ` Jason Gunthorpe
2020-05-01 22:31       ` Dey, Megha
2020-05-03 22:22         ` Jason Gunthorpe
2020-05-03 22:31           ` Dey, Megha
2020-05-03 22:36             ` Jason Gunthorpe
2020-05-04  0:20               ` Dey, Megha
2020-04-22 23:04   ` Dey, Megha
2020-04-23 19:44     ` Jason Gunthorpe
2020-05-01 22:32       ` Dey, Megha [this message]
2020-04-24  6:31   ` Jason Wang

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