From: David Laight <David.Laight@ACULAB.COM>
To: 'Arnd Bergmann' <arnd@arndb.de>,
Linus Walleij <linus.walleij@linaro.org>
Cc: "Allen Pais" <apais@linux.microsoft.com>,
"Vincent Guittot" <vincent.guittot@linaro.org>,
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Subject: RE: [RFC 1/1] drivers/dma/*: replace tasklets with workqueue
Date: Wed, 25 May 2022 15:14:55 +0000 [thread overview]
Message-ID: <9947cfa64667406996de191f07b9e8b9@AcuMS.aculab.com> (raw)
In-Reply-To: <CAK8P3a0j_rziihsgHnG5bHMxmPbOkAhT6_+CCE4iFZy7HzQrLw@mail.gmail.com>
From: Arnd Bergmann
> Sent: 25 May 2022 12:04
>
> On Wed, May 25, 2022 at 11:24 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> > On Tue, Apr 19, 2022 at 11:17 PM Allen Pais <apais@linux.microsoft.com> wrote:
> >
> > > The tasklet is an old API which will be deprecated, workqueue API
> > > cab be used instead of them.
> > >
> > > This patch replaces the tasklet usage in drivers/dma/* with a
> > > simple work.
> > >
> > > Github: https://github.com/KSPP/linux/issues/94
> > >
> > > Signed-off-by: Allen Pais <apais@linux.microsoft.com>
> >
> > Paging Vincent Guittot and Arnd Bergmann on the following question
> > on this patch set:
> >
> > - Will replacing tasklets with workque like this negatively impact the
> > performance on DMA engine bottom halves?
>
> I think it will in some cases but not others. The problem I see is that
> the short patch description makes it sound like a trivial conversion of a
> single subsystem, but in reality this interacts with all the drivers using
> DMA engines, including tty/serial, sound, mmc and spi.
>
> In many cases, the change is an improvement, but I can see a number
> of ways this might go wrong:
If the 'tasklet' API is based on the softint (or similar)
then changing to workqueue will cause serious grief in many cases
unless the workqueue process runs at a high priority.
Currently softint callbacks are usually higher priority than
any task/process.
So on a busy system they almost always run.
(They can get caught out by a need_resched() call and suddenly
be fighting with normal user processes for cpu time.)
As arnd said, I suspect this will break anything using tasklets
to chain together audio or video buffers.
Any process code doing that would need probbaly to run at a
'middling' RT priority.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-05-25 15:15 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-19 21:16 [RFC 0/1] refactor all tasklet users into other APIs Allen Pais
2022-04-19 21:16 ` [RFC 1/1] drivers/dma/*: replace tasklets with workqueue Allen Pais
2022-04-20 2:31 ` Kees Cook
2022-04-22 16:48 ` Allen Pais
2022-04-25 15:06 ` Linus Walleij
2022-04-25 23:59 ` Allen Pais
2022-04-25 15:56 ` Krzysztof Kozlowski
2022-04-25 19:55 ` Gustavo A. R. Silva
2022-04-28 9:29 ` Andy Shevchenko
[not found] ` <DA101ED8-F99F-4DCB-9CB7-370A62C44B65@linux.microsoft.com>
2022-05-12 21:54 ` Linus Walleij
2022-05-16 11:40 ` Vinod Koul
2022-04-26 0:04 ` Allen Pais
2022-04-27 2:45 ` Vinod Koul
2022-04-27 15:20 ` Dave Jiang
2022-04-27 15:58 ` Allen Pais
2022-04-27 15:53 ` Allen Pais
2022-05-25 9:24 ` Linus Walleij
2022-05-25 9:52 ` Vincent Guittot
2022-05-25 11:03 ` Arnd Bergmann
2022-05-25 15:14 ` David Laight [this message]
[not found] ` <6E248F41-6687-4F2B-B847-DB5459BA1344@linux.microsoft.com>
2022-05-25 17:48 ` Arnd Bergmann
2022-05-25 18:04 ` Allen Pais
2022-05-27 8:06 ` Vinod Koul
2022-05-27 10:59 ` Arnd Bergmann
2022-05-31 6:56 ` Vinod Koul
[not found] ` <0A9EDEDC-9E6C-47F8-89C0-48DCDD3F9DE3@linux.microsoft.com>
2022-05-31 18:02 ` Arnd Bergmann
2022-05-31 18:19 ` Allen Pais
2022-05-31 19:27 ` Arnd Bergmann
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