From: Dmitry Osipenko <digetx@gmail.com>
To: Alexandre Courbot <acourbot@chromium.org>,
Tomasz Figa <tfiga@chromium.org>
Cc: Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Hans Verkuil <hverkuil@xs4all.nl>,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
Pawel Osciak <posciak@chromium.org>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Sakari Ailus <sakari.ailus@linux.intel.com>,
Gustavo Padovan <gustavo.padovan@collabora.com>,
Linux Media Mailing List <linux-media@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Maxime Ripard <maxime.ripard@bootlin.com>
Subject: Re: [RFCv4,19/21] media: vim2m: add request support
Date: Mon, 12 Mar 2018 17:44:54 +0300 [thread overview]
Message-ID: <c2a2e158-aa02-f16a-400e-6bde5f78cba1@gmail.com> (raw)
In-Reply-To: <CAPBb6MXYj0SHUWPRuCNewUetmxrePx1NFQfB6tw+BbPHS+Hkmg@mail.gmail.com>
On 12.03.2018 15:32, Alexandre Courbot wrote:
> On Mon, Mar 12, 2018 at 5:15 PM, Tomasz Figa <tfiga@chromium.org> wrote:
>> Hi Paul, Dmitry,
>>
>> On Mon, Mar 12, 2018 at 5:10 PM, Paul Kocialkowski
>> <paul.kocialkowski@bootlin.com> wrote:
>>> Hi,
>>>
>>> On Sun, 2018-03-11 at 22:42 +0300, Dmitry Osipenko wrote:
>>>> Hello,
>>>>
>>>> On 07.03.2018 19:37, Paul Kocialkowski wrote:
>>>>> Hi,
>>>>>
>>>>> First off, I'd like to take the occasion to say thank-you for your
>>>>> work.
>>>>> This is a major piece of plumbing that is required for me to add
>>>>> support
>>>>> for the Allwinner CedarX VPU hardware in upstream Linux. Other
>>>>> drivers,
>>>>> such as tegra-vde (that was recently merged in staging) are also
>>>>> badly
>>>>> in need of this API.
>>>>
>>>> Certainly it would be good to have a common UAPI. Yet I haven't got my
>>>> hands on
>>>> trying to implement the V4L interface for the tegra-vde driver, but
>>>> I've taken a
>>>> look at Cedrus driver and for now I've one question:
>>>>
>>>> Would it be possible (or maybe already is) to have a single IOCTL that
>>>> takes input/output buffers with codec parameters, processes the
>>>> request(s) and returns to userspace when everything is done? Having 5
>>>> context switches for a single frame decode (like Cedrus VAAPI driver
>>>> does) looks like a bit of overhead.
>>>
>>> The V4L2 interface exposes ioctls for differents actions and I don't
>>> think there's a combined ioctl for this. The request API was introduced
>>> precisely because we need to have consistency between the various ioctls
>>> needed for each frame. Maybe one single (atomic) ioctl would have worked
>>> too, but that's apparently not how the V4L2 API was designed.
>>>
>>> I don't think there is any particular overhead caused by having n ioctls
>>> instead of a single one. At least that would be very surprising IMHO.
>>
>> Well, there is small syscall overhead, which normally shouldn't be
>> very painful, although with all the speculative execution hardening,
>> can't be sure of anything anymore. :)
>>
>> Hans and Alex can correct me if I'm wrong, but I believe there is a
>> more atomic-like API being planned, which would only need one IOCTL to
>> do everything. However, that would be a more serious change to the
>> V4L2 interfaces, so should be decoupled from Request API itself.
>
> Indeed, we discussed the possibility to setup and submit requests in
> one syscall, similarly (at least in spirit) to the DRM atomic API.
>
> This has only been discussed though, and as a feature to consider
> *after* the request API is merged for codecs (as the more complex
> camera use-cases would benefit more from it). As Tomasz mentioned, the
> overhead of ioctls is somehow negligible compared to the workload of
> the encoding/decoding itself, although I suppose it can still add up.
> The main advantage I can see for this is a simpler and less
> error-prone setup of requests for user-space.
Indeed, atomic API should be nicer from a userspace perspective and a bit more
optimal for at least some of workloads. Would be good to have it.
next prev parent reply other threads:[~2018-03-12 14:45 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-20 4:44 [RFCv4 00/21] Request API Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 01/21] media: add request API core and UAPI Alexandre Courbot
2018-02-20 10:36 ` Hans Verkuil
2018-02-21 6:01 ` Alexandre Courbot
2018-02-21 7:29 ` Hans Verkuil
2018-02-22 9:30 ` Alexandre Courbot
2018-02-22 9:38 ` Hans Verkuil
2018-02-20 4:44 ` [RFCv4 02/21] v4l2-ctrls: v4l2_ctrl_add_handler: add from_other_dev Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 03/21] v4l2-ctrls: prepare internal structs for request API Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 04/21] v4l2-ctrls: add core " Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 05/21] v4l2-ctrls: use ref in helper instead of ctrl Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 06/21] v4l2-ctrls: support g/s_ext_ctrls for requests Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 07/21] v4l2-ctrls: add v4l2_ctrl_request_setup Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 08/21] [WAR] v4l2-ctrls: do not clone non-standard controls Alexandre Courbot
2018-02-20 13:05 ` Hans Verkuil
2018-02-20 4:44 ` [RFCv4 09/21] v4l2: add request API support Alexandre Courbot
2018-02-20 7:36 ` Philippe Ombredanne
2018-02-20 8:03 ` Alexandre Courbot
2018-02-20 13:25 ` Hans Verkuil
2018-02-21 6:01 ` Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 10/21] videodev2.h: Add request_fd field to v4l2_buffer Alexandre Courbot
2018-02-20 15:20 ` Hans Verkuil
2018-02-21 6:01 ` Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 11/21] media: v4l2_fh: add request entity field Alexandre Courbot
2018-02-20 15:24 ` Hans Verkuil
2018-02-21 6:01 ` Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 12/21] media: videobuf2: add support for requests Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 13/21] media: videobuf2-v4l2: " Alexandre Courbot
2018-02-20 16:18 ` Hans Verkuil
2018-02-21 6:01 ` Alexandre Courbot
2018-02-23 6:34 ` Tomasz Figa
2018-02-23 7:21 ` Hans Verkuil
2018-02-23 7:33 ` Tomasz Figa
2018-02-23 7:43 ` Hans Verkuil
2018-03-07 16:50 ` [RFCv4,13/21] " Paul Kocialkowski
2018-03-08 13:50 ` Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 14/21] videodev2.h: add request_fd field to v4l2_ext_controls Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 15/21] v4l2-ctrls: support requests in EXT_CTRLS ioctls Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 16/21] v4l2: video_device: support for creating requests Alexandre Courbot
2018-02-20 16:35 ` Hans Verkuil
2018-02-21 6:01 ` Alexandre Courbot
2018-02-21 7:37 ` Hans Verkuil
2018-02-20 4:44 ` [RFCv4 17/21] media: mem2mem: support for requests Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 18/21] Documentation: v4l: document request API Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 19/21] media: vim2m: add request support Alexandre Courbot
2018-03-07 16:37 ` [RFCv4,19/21] " Paul Kocialkowski
2018-03-08 13:48 ` Alexandre Courbot
2018-03-09 14:35 ` Paul Kocialkowski
2018-03-13 10:24 ` Alexandre Courbot
2018-03-14 13:25 ` Paul Kocialkowski
2018-03-19 9:17 ` Alexandre Courbot
2018-03-11 19:40 ` Dmitry Osipenko
2018-03-11 19:42 ` Dmitry Osipenko
2018-03-12 8:10 ` Paul Kocialkowski
2018-03-12 8:15 ` Tomasz Figa
2018-03-12 8:25 ` Paul Kocialkowski
2018-03-12 8:29 ` Tomasz Figa
2018-03-12 12:21 ` Dmitry Osipenko
2018-03-12 12:32 ` Alexandre Courbot
2018-03-12 14:44 ` Dmitry Osipenko [this message]
2018-02-20 4:44 ` [RFCv4 20/21] media: vivid: add request support for the video capture device Alexandre Courbot
2018-02-20 4:44 ` [RFCv4 21/21] [WIP] media: media-device: support for creating requests Alexandre Courbot
2018-02-20 4:54 ` [RFCv4 00/21] Request API Alexandre Courbot
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