From: Parav Pandit <parav@mellanox.com>
To: Kirti Wankhede <kwankhede@nvidia.com>,
Alex Williamson <alex.williamson@redhat.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"cohuck@redhat.com" <cohuck@redhat.com>,
"cjia@nvidia.com" <cjia@nvidia.com>
Subject: RE: [PATCH v2 0/2] Simplify mtty driver and mdev core
Date: Tue, 13 Aug 2019 14:40:02 +0000 [thread overview]
Message-ID: <AM0PR05MB4866993536C0C8ACEA2F92DBD1D20@AM0PR05MB4866.eurprd05.prod.outlook.com> (raw)
In-Reply-To: <77ffb1f8-e050-fdf5-e306-0a81614f7a88@nvidia.com>
> -----Original Message-----
> From: Kirti Wankhede <kwankhede@nvidia.com>
> Sent: Monday, August 12, 2019 5:06 PM
> To: Alex Williamson <alex.williamson@redhat.com>; Parav Pandit
> <parav@mellanox.com>
> Cc: kvm@vger.kernel.org; linux-kernel@vger.kernel.org; cohuck@redhat.com;
> cjia@nvidia.com
> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
>
>
>
> On 8/9/2019 4:32 AM, Alex Williamson wrote:
> > On Thu, 8 Aug 2019 09:12:53 -0500
> > Parav Pandit <parav@mellanox.com> wrote:
> >
> >> Currently mtty sample driver uses mdev state and UUID in convoluated
> >> way to generate an interrupt.
> >> It uses several translations from mdev_state to mdev_device to mdev uuid.
> >> After which it does linear search of long uuid comparision to find
> >> out mdev_state in mtty_trigger_interrupt().
> >> mdev_state is already available while generating interrupt from which
> >> all such translations are done to reach back to mdev_state.
> >>
> >> This translations are done during interrupt generation path.
> >> This is unnecessary and reduandant.
> >
> > Is the interrupt handling efficiency of this particular sample driver
> > really relevant, or is its purpose more to illustrate the API and
> > provide a proof of concept? If we go to the trouble to optimize the
> > sample driver and remove this interface from the API, what do we lose?
> >
> > This interface was added via commit:
> >
> > 99e3123e3d72 vfio-mdev: Make mdev_device private and abstract
> > interfaces
> >
> > Where the goal was to create a more formal interface and abstract
> > driver access to the struct mdev_device. In part this served to make
> > out-of-tree mdev vendor drivers more supportable; the object is
> > considered opaque and access is provided via an API rather than
> > through direct structure fields.
> >
> > I believe that the NVIDIA GRID mdev driver does make use of this
> > interface and it's likely included in the sample driver specifically
> > so that there is an in-kernel user for it (ie. specifically to avoid
> > it being removed so casually). An interesting feature of the NVIDIA
> > mdev driver is that I believe it has portions that run in userspace.
> > As we know, mdevs are named with a UUID, so I can imagine there are
> > some efficiencies to be gained in having direct access to the UUID for
> > a device when interacting with userspace, rather than repeatedly
> > parsing it from a device name.
>
> That's right.
>
> > Is that really something we want to make more difficult in order to
> > optimize a sample driver? Knowing that an mdev device uses a UUID for
> > it's name, as tools like libvirt and mdevctl expect, is it really
> > worthwhile to remove such a trivial API?
> >
> >> Hence,
> >> Patch-1 simplifies mtty sample driver to directly use mdev_state.
> >>
> >> Patch-2, Since no production driver uses mdev_uuid(), simplifies and
> >> removes redandant mdev_uuid() exported symbol.
> >
> > s/no production driver/no in-kernel production driver/
> >
> > I'd be interested to hear how the NVIDIA folks make use of this API
> > interface. Thanks,
> >
>
> Yes, NVIDIA mdev driver do use this interface. I don't agree on removing
> mdev_uuid() interface.
>
We need to ask Greg or Linus on the kernel policy on whether an API should exist without in-kernel driver.
We don't add such API in netdev, rdma and possibly other subsystem.
Where can we find this mdev driver in-tree?
next prev parent reply other threads:[~2019-08-13 14:40 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-02 6:59 [PATCH 0/2] Simplify mtty driver and mdev core Parav Pandit
2019-08-02 6:59 ` [PATCH 1/2] vfio-mdev/mtty: Simplify interrupt generation Parav Pandit
2019-08-06 8:15 ` Cornelia Huck
2019-08-02 6:59 ` [PATCH 2/2] vfio/mdev: Removed unused and redundant API for mdev name Parav Pandit
2019-08-06 8:29 ` Cornelia Huck
2019-08-06 13:12 ` Parav Pandit
2019-08-06 14:18 ` [PATCH v1 0/2] Simplify mtty driver and mdev core Parav Pandit
2019-08-06 14:18 ` [PATCH v1 1/2] vfio-mdev/mtty: Simplify interrupt generation Parav Pandit
2019-08-06 14:18 ` [PATCH v1 2/2] vfio/mdev: Removed unused and redundant API for mdev UUID Parav Pandit
2019-08-07 9:28 ` Cornelia Huck
2019-08-07 16:33 ` Parav Pandit
2019-08-08 8:29 ` Cornelia Huck
2019-08-08 14:01 ` Parav Pandit
2019-08-08 14:12 ` [PATCH v2 0/2] Simplify mtty driver and mdev core Parav Pandit
2019-08-08 14:12 ` [PATCH v2 1/2] vfio-mdev/mtty: Simplify interrupt generation Parav Pandit
2019-08-13 16:39 ` Christoph Hellwig
2019-08-23 20:48 ` Alex Williamson
2019-08-08 14:12 ` [PATCH v2 2/2] vfio/mdev: Removed unused and redundant API for mdev UUID Parav Pandit
2019-08-13 16:39 ` Christoph Hellwig
2019-08-16 15:22 ` Cornelia Huck
2019-08-08 23:02 ` [PATCH v2 0/2] Simplify mtty driver and mdev core Alex Williamson
2019-08-09 8:07 ` Cornelia Huck
2019-08-12 11:35 ` Kirti Wankhede
2019-08-13 14:40 ` Parav Pandit [this message]
2019-08-13 14:52 ` Alex Williamson
2019-08-13 16:28 ` Parav Pandit
2019-08-13 16:34 ` Cornelia Huck
2019-08-13 17:11 ` Alex Williamson
2019-08-14 5:54 ` Parav Pandit
2019-08-14 8:01 ` Cornelia Huck
2019-08-14 12:27 ` Parav Pandit
2019-08-14 13:09 ` Cornelia Huck
2019-08-14 13:45 ` Parav Pandit
2019-08-14 14:57 ` Alex Williamson
2019-08-14 16:21 ` Parav Pandit
2019-08-20 8:58 ` Parav Pandit
2019-08-20 9:58 ` Christophe de Dinechin
2019-08-20 11:25 ` Parav Pandit
2019-08-20 16:31 ` Cornelia Huck
2019-08-21 2:42 ` Parav Pandit
2019-08-20 17:19 ` Alex Williamson
2019-08-20 17:55 ` Cornelia Huck
2019-08-21 3:57 ` Parav Pandit
2019-08-21 3:42 ` Parav Pandit
2019-08-21 4:20 ` Alex Williamson
2019-08-21 4:40 ` Parav Pandit
2019-08-21 4:57 ` Alex Williamson
2019-08-21 5:01 ` Parav Pandit
2019-08-21 5:26 ` Alex Williamson
2019-08-21 6:23 ` Parav Pandit
2019-08-22 9:29 ` Jiri Pirko
2019-08-22 9:42 ` Parav Pandit
2019-08-22 9:58 ` Jiri Pirko
2019-08-22 10:04 ` Parav Pandit
2019-08-22 12:19 ` Jiri Pirko
2019-08-22 13:33 ` Parav Pandit
2019-08-23 8:12 ` Jiri Pirko
2019-08-23 8:14 ` Parav Pandit
2019-08-23 14:28 ` Alex Williamson
2019-08-23 14:53 ` Parav Pandit
2019-08-23 15:04 ` Jiri Pirko
2019-08-23 15:52 ` Alex Williamson
2019-08-23 16:14 ` Parav Pandit
2019-08-23 17:16 ` Alex Williamson
2019-08-23 18:00 ` Parav Pandit
2019-08-23 19:43 ` Alex Williamson
2019-08-24 3:56 ` Parav Pandit
2019-08-24 4:45 ` Parav Pandit
2019-08-24 4:59 ` Alex Williamson
2019-08-24 5:22 ` Parav Pandit
2019-08-13 16:37 ` Christoph Hellwig
2019-08-13 17:40 ` Greg Kroah-Hartman
2019-08-14 5:30 ` Parav Pandit
2019-08-13 14:48 ` Parav Pandit
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