From: Parav Pandit <parav@mellanox.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"kwankhede@nvidia.com" <kwankhede@nvidia.com>,
"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 14:48:23 +0000 [thread overview]
Message-ID: <AM0PR05MB48661804F69F24B08036E57DD1D20@AM0PR05MB4866.eurprd05.prod.outlook.com> (raw)
In-Reply-To: <20190808170247.1fc2c4c4@x1.home>
Hi Alex,
> -----Original Message-----
> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Friday, August 9, 2019 4:33 AM
> To: Parav Pandit <parav@mellanox.com>
> Cc: kvm@vger.kernel.org; kwankhede@nvidia.com; linux-
> kernel@vger.kernel.org; cohuck@redhat.com; cjia@nvidia.com
> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
>
> 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.
>
This is not the common practice in the kernel to provide exported symbol for every single field of the structure.
> 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.
Can you please point to the kernel code that accesses the UUID?
> 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?
>
Yes. it is worthwhile to not keep any dead code in the kernel when there is no in-kernel driver using it.
Did I miss a caller?
Sample driver is setting wrong example of how/when uuid is used.
There has be better example to show how/when/why to use it.
Out of tree driver doesn't qualify API addition to my understanding.
I like to listen to Greg and others for an API inclusion without user as I haven't come across such practice in other subsystems such as nvme, netdev, rdma.
> > 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,
>
> Alex
>
> > ---
> > Changelog:
> > v1->v2:
> > - Corrected email of Kirti
> > - Updated cover letter commit log to address comment from Cornelia
> > - Added Reviewed-by tag
> > v0->v1:
> > - Updated commit log
> >
> > Parav Pandit (2):
> > vfio-mdev/mtty: Simplify interrupt generation
> > vfio/mdev: Removed unused and redundant API for mdev UUID
> >
> > drivers/vfio/mdev/mdev_core.c | 6 ------
> > include/linux/mdev.h | 1 -
> > samples/vfio-mdev/mtty.c | 39 +++++++----------------------------
> > 3 files changed, 8 insertions(+), 38 deletions(-)
> >
prev parent reply other threads:[~2019-08-13 14:48 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
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 [this message]
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