From: Arnd Bergmann > Sent: 25 May 2022 12:04 > > On Wed, May 25, 2022 at 11:24 AM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > > On Tue, Apr 19, 2022 at 11:17 PM Allen Pais <apais@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx> > > > > 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)
