From: Cornelia Huck <cohuck@redhat.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Parav Pandit <parav@mellanox.com>,
kvm@vger.kernel.org, kwankhede@nvidia.com,
linux-kernel@vger.kernel.org, cjia@nvidia.com
Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
Date: Fri, 9 Aug 2019 10:07:14 +0200 [thread overview]
Message-ID: <20190809100714.6b012f41.cohuck@redhat.com> (raw)
In-Reply-To: <20190808170247.1fc2c4c4@x1.home>
On Thu, 8 Aug 2019 17:02:47 -0600
Alex Williamson <alex.williamson@redhat.com> 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?
Not sure how useful the sample driver is as a template; blindly copying
their interrupt handling is probably not a good idea.
>
> 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. 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?
Ripping out the uuid is a bad idea, I agree. The device name simply is
no good replacement for that.
If there's a good use case for using the uuid in a vendor driver, let's
keep the accessor. But then we probably should either leave the sample
driver alone, or add a more compelling use of the api there.
>
> > 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(-)
> >
>
next prev parent reply other threads:[~2019-08-09 8:07 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 [this message]
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
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