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From: "Dey, Megha" <megha.dey@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>, Jason Gunthorpe <jgg@mellanox.com>
Cc: Marc Zyngier <maz@kernel.org>,
	"Jiang, Dave" <dave.jiang@intel.com>,
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	"Liu, Yi L" <yi.l.liu@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, 6 Aug 2020 10:58:45 -0700
Message-ID: <014ffe59-38d3-b770-e065-dfa2d589adc6@intel.com> (raw)
In-Reply-To: <87tuxfhf9u.fsf@nanos.tec.linutronix.de>

Hi Thomas,

On 8/6/2020 10:10 AM, Thomas Gleixner wrote:
> 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?

oops, i hope i have fixed it now..

>
>>>>> 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 a lot Thomas for this detailed explanation!!

The dev-msi domain can be used by other devices if they too would want 
to follow the
vector->intel IR->dev-msi IRQ hierarchy.
I do create one dev-msi IRQ domain instance per IR unit. So I guess for 
this case,
it makes most sense to have a dev-msi IRQ domain per IR unit as opposed 
to create one
per individual driver..
>
> Thanks,
>
>          tglx

  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
2020-08-06 17:58                       ` Dey, Megha [this message]
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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