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From: Thomas Gleixner <tglx@linutronix.de>
To: "Dey\, Megha" <megha.dey@intel.com>, Jason Gunthorpe <jgg@mellanox.com>
Cc: Marc Zyngier <maz@kernel.org>, "Jiang\,
	Dave" <dave.jiang@intel.com>,
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Subject: RE: [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI irq domain
Date: Thu, 06 Aug 2020 19:10:05 +0200
Message-ID: <87tuxfhf9u.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <c6a1c065ab9b46bbaf9f5713462085a5@intel.com>

Megha,

"Dey, Megha" <megha.dey@intel.com> writes:

>> -----Original Message-----
>> From: Jason Gunthorpe <jgg@mellanox.com>
<SNIP>
>> Subject: Re: [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI
>> irq domain

can you please fix your mail client not to copy the whole header of the
mail you are replying to into the mail body?

>> > > Well, I had suggested to pass in the parent struct device, but it
>> Oops, I was thinking of platform_msi_domain_alloc_irqs() not
>> create_device_domain()
>> 
>> ie call it in the device driver that wishes to consume the extra MSIs.
>> 
>> Is there a harm if each device driver creates a new irq_domain for its use?
>
> Well, the only harm is if we want to reuse the irq domain.

You cannot reuse the irq domain if you create a domain per driver. The
way how hierarchical domains work is:

vector --- DMAR-MSI
       |
       |-- ....
       |
       |-- IR-0 --- IO/APIC-0
       |        | 
       |        |-- IO/APIC-1
       |        |
       |        |-- PCI/MSI-0
       |        |
       |        |-- HPET/MSI-0
       |
       |-- IR-1 --- PCI/MSI-1
       |        |

The outermost domain is what the actual device driver uses. I.e. for
PCI-MSI it's the msi domain which is associated to the bus the device is
connected to. Each domain has its own interrupt chip instance and its
own data set.

Domains of the same type share the code, but neither the data nor the
interrupt chip instance.

Also there is a strict parent child relationship in terms of resources.
Let's look at PCI.

PCI/MSI-0 depends on IR-0 which depends on the vector domain. That's
reflecting both the flow of the interrupt and the steps required for
various tasks, e.g. allocation/deallocation and also interrupt chip
operations. In order to allocate a PCI/MSI interrupt in domain PCI/MSI-0
a slot in the remapping unit and a vector needs to be allocated.

If you disable interrupt remapping all the outermost domains in the
scheme above become childs of the vector domain.

So if we look at DEV/MSI as a infrastructure domain then the scheme
looks like this:

vector --- DMAR-MSI
       |
       |-- ....
       |
       |-- IR-0 --- IO/APIC-0
       |        | 
       |        |-- IO/APIC-1
       |        |
       |        |-- PCI/MSI-0
       |        |
       |        |-- HPET/MSI-0
       |        |
       |        |-- DEV/MSI-0
       |
       |-- IR-1 --- PCI/MSI-1
       |        |
       |        |-- DEV/MSI-1


But if you make it per device then you have multiple DEV/MSI domains per
IR unit.

What's the right thing to do?

If the DEV/MSI domain has it's own per IR unit resource management, then
you need one per IR unit.

If the resource management is solely per device then having a domain per
device is the right choice.

Thanks,

        tglx

  parent reply index

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 [this message]
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
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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