6 ms·

Obligatory: “ I repeat: do not use spinlocks in user space, unless you actually know what you're doing. And be aware that the likelihood that you know what you

Obligatory: “ I repeat: do not use spinlocks in user space, unless you actually know what you're doing. And be aware that the likelihood that you know what you are doing is basically nil.” https://www.realworldtech.com/forum/?threadid=189711&curpostid=189723 https://www.realworldtech.com/forum/?threadid=189711&curpost...

bobowzki 4y ago
Exactly what I thought too. Thanks for posting!
spacechild1 4y ago
Spinlocks can be useful in multi-threaded real-time audio code. Audio processing has to meet tight deadlines (in the order of a few milliseconds) and the thread(s) must not be preempted/rescheduled, so traditional mutexes are off the table. (Here's a good introduction to the topic: http://www.rossbencina.com/code/real-time-audio-programming-101-time-waits-for-nothing http://www.rossbencina.com/code/real-time-audio-programming-...) Now, let's say several threads have to write their results into a common buffer. Ideally, they would first write into individual buffers which you can safely sum after a synchronization point. However, depending on the architecture, this might not always be possible and a spinlock might be the only practical solution. Note again that audio threads typically run with real-time priority and should not be preempted, so the major issues with spinlocks - that Linus correctly points out! - don't apply, AFAICT. One example for audio software that uses spinlocks is "Supernova", a multi-threaded reimplementation of the "scsynth" audio server. Here the author describes the locking strategy: https://www.complang.tuwien.ac.at/Diplomarbeiten/blechmann11.pdf https://www.complang.tuwien.ac.at/Diplomarbeiten/blechmann11... (section 4.3)
- muziq 4y ago
- amihav 4y ago
  Great comment! I agree - but still its good practice to understand and know how to implement it.
deleted 4y ago
[deleted]
warinukraine 4y ago
Can someone clarify the meaning of "spinning" in Linus's post?
- buildartefact 4y ago
  It was in response to this blog post: https://probablydance.com/2019/12/30/measuring-mutexes-spinlocks-and-how-bad-the-linux-scheduler-really-is/ https://probablydance.com/2019/12/30/measuring-mutexes-spinl... Basically your standard CAS loop with _mm_pause() to yield.

bobowzki 4y ago

Exactly what I thought too. Thanks for posting!

spacechild1 4y ago

Spinlocks can be useful in multi-threaded real-time audio code. Audio processing has to meet tight deadlines (in the order of a few milliseconds) and the thread(s) must not be preempted/rescheduled, so traditional mutexes are off the table. (Here's a good introduction to the topic: http://www.rossbencina.com/code/real-time-audio-programming-101-time-waits-for-nothing http://www.rossbencina.com/code/real-time-audio-programming-...) Now, let's say several threads have to write their results into a common buffer. Ideally, they would first write into individual buffers which you can safely sum after a synchronization point. However, depending on the architecture, this might not always be possible and a spinlock might be the only practical solution. Note again that audio threads typically run with real-time priority and should not be preempted, so the major issues with spinlocks - that Linus correctly points out! - don't apply, AFAICT. One example for audio software that uses spinlocks is "Supernova", a multi-threaded reimplementation of the "scsynth" audio server. Here the author describes the locking strategy: https://www.complang.tuwien.ac.at/Diplomarbeiten/blechmann11.pdf https://www.complang.tuwien.ac.at/Diplomarbeiten/blechmann11... (section 4.3)

muziq 4y ago
amihav 4y ago
Great comment! I agree - but still its good practice to understand and know how to implement it.

deleted 4y ago

[deleted]

warinukraine 4y ago

Can someone clarify the meaning of "spinning" in Linus's post?

buildartefact 4y ago
It was in response to this blog post: https://probablydance.com/2019/12/30/measuring-mutexes-spinlocks-and-how-bad-the-linux-scheduler-really-is/ https://probablydance.com/2019/12/30/measuring-mutexes-spinl... Basically your standard CAS loop with _mm_pause() to yield.