Realtime preemption locking core merged

[Posted August 31, 2021 by corbet]

The 5.15 merge window is off to a fast start; stay tuned for our usual full summary. It is worth mentioning, though, that the realtime preemption locking code has been pulled into the mainline with little fanfare. This work began in 2004 and has fundamentally changed many parts of the core kernel. With this pull, the sleepable locks that make deterministic realtime response possible have finally joined all of that other work (though the kernel must be built with the REALTIME configuration option to use them).

Congratulations are due to all of the realtime developers who pushed this project forward for nearly two decades.

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Realtime preemption locking core merged

Posted Aug 31, 2021 15:56 UTC (Tue) by jcm (subscriber, #18262) [Link]

This is an awesome piece of news. Congrats to everyone!

Realtime preemption locking core merged

Posted Aug 31, 2021 16:08 UTC (Tue) by smurf (subscriber, #17840) [Link]

Nice. So what's left in the realtime stack? Any interesting remaining problems, or just a heap of tidbits to clean up?

Realtime preemption locking core merged

Posted Sep 1, 2021 20:01 UTC (Wed) by tglx (subscriber, #31301) [Link]

The remaining larger pieces are:

- memory management: The bulk of those changes sits in the akpm tree and hopefully makes 5.15-rc1

- printk: Another batch is destined for 5.15-rc1, but we still have a few steps to overcome there. Most of the technical issues have been solved, but there are quite some details to sort

- fs/namespace: The last trylock loop which causes headache. A few attempts have been made before and we're still twisting our brains around it

The rest is the tail of small changes here and there, but nothing fundamental anymore.

Realtime preemption locking core merged

Posted Aug 31, 2021 17:15 UTC (Tue) by q_q_p_p (subscriber, #131113) [Link]

This preemption model is not available on any of the archs yet, right ? I wanted to try it, but it's not shown in the menuconfig and it seems no arch sets ARCH_SUPPORTS_RT=y

Spectacular!

Posted Aug 31, 2021 17:26 UTC (Tue) by david.a.wheeler (guest, #72896) [Link]

This is great news! There are a lot of situations where you need a real-time OS, yet you're able to accept the hardware requirements (such as memory size) of a kernel like Linux. This will open up the Linux kernel to many more potential uses.

I presume there's going to be more to do to make this "useful" to many. I hope there will be an LWN.net article about what are the next important things to do for real-time on Linux :-).

Spectacular!

Posted Sep 1, 2021 18:13 UTC (Wed) by clump (subscriber, #27801) [Link]

Realtime really helps when recording audio with Linux. The stock kernel is usually quite good but you can often get better latency with realtime kernels. Hopefully this makes life easier for mainstream Linux distributions.

Realtime preemption locking core merged

Posted Aug 31, 2021 18:34 UTC (Tue) by fhuberts (subscriber, #64683) [Link]

Insanely awesome work!
And even more awesome that the developers stuck with it for so long.

This is absolutely a huge milestone, even though we're not there yet, we so very close now!

This is going to have a major impact if distribution are going to provide RT kernels soon: interactivity of desktops, audio/video workstation, real-time data processing applications. There are so many use-case that can benefit from this!

Realtime preemption locking core merged

Posted Aug 31, 2021 18:36 UTC (Tue) by fhuberts (subscriber, #64683) [Link]

That's a lot of typos :-(
Too hyped I guess.

Phoronix info

Posted Aug 31, 2021 23:16 UTC (Tue) by david.a.wheeler (guest, #72896) [Link]

Phoronix has a little additional information here:

https://www.phoronix.com/scan.php?page=news_item&px=P...

Realtime preemption locking core merged

Posted Sep 2, 2021 1:44 UTC (Thu) by lordgilman (subscriber, #60767) [Link]

With the merging of the realtime patch set Linux is now complete. Thanks to everyone who participated.