4 ms·

No, linux pessimizes for that case if you do not cooperate with the scheduler. You can implement spinlocks in userspace under specific circumstances. You will

No, linux pessimizes for that case if you do not cooperate with the scheduler. You can implement spinlocks in userspace under specific circumstances. You will need to mark your threads as realtime threads[0] and have a fallback to futex if the fast path (spinning) doesn't work out. And even then you need to benchmark on multiple machines and with realistic workloads (not microbenchmarks) to see whether it's actually worth it for your application. It's complex, linus goes into more detail here[1] [0] http://man7.org/linux/man-pages/man3/pthread_spin_init.3.html#NOTES http://man7.org/linux/man-pages/man3/pthread_spin_init.3.htm... [1] https://www.realworldtech.com/forum/?threadid=189711&curpostid=189755 https://www.realworldtech.com/forum/?threadid=189711&curpost...

shadowgovt 7y ago
Do Windows, MacOS/iOS, and console OS's treat spinlocks more friendly than Linux?
- CoolGuySteve 7y ago
  In Windows, CriticalSection can spin for a user-defined period of time, which is more or less what you want. Although it would probably make more sense for it to have a "spin until my quantum is over" option because how is the caller supposed to know that? https://docs.microsoft.com/en-us/cpp/cppcx/wrl/criticalsection-class?view=vs-2019#criticalsection https://docs.microsoft.com/en-us/cpp/cppcx/wrl/criticalsecti...
quotemstr 7y ago
If you have a fallback to futex, then what you have isn't a spinlock, but an adaptive mutex (which spins, then blocks). Lots of operating systems have those already and you don't need to build your own.
- shaklee3 7y ago
  Or just use a futex alone, since that mimics its behavior enough.
- the8472 7y ago
  If you really want to use a pure spinlock you'll either have to accept that worst-case behavior being worse than a mutex or you have to jump through a lot of hoops (pinning threads, isolating cores, reassigning interrupts) to make sure you don't get descheduled. Because the scheduler won't know anything about priority inversions or even waiting threads, they all look runnable.

shadowgovt 7y ago

Do Windows, MacOS/iOS, and console OS's treat spinlocks more friendly than Linux?

CoolGuySteve 7y ago
In Windows, CriticalSection can spin for a user-defined period of time, which is more or less what you want. Although it would probably make more sense for it to have a "spin until my quantum is over" option because how is the caller supposed to know that? https://docs.microsoft.com/en-us/cpp/cppcx/wrl/criticalsection-class?view=vs-2019#criticalsection https://docs.microsoft.com/en-us/cpp/cppcx/wrl/criticalsecti...

quotemstr 7y ago

If you have a fallback to futex, then what you have isn't a spinlock, but an adaptive mutex (which spins, then blocks). Lots of operating systems have those already and you don't need to build your own.

shaklee3 7y ago
Or just use a futex alone, since that mimics its behavior enough.
the8472 7y ago
If you really want to use a pure spinlock you'll either have to accept that worst-case behavior being worse than a mutex or you have to jump through a lot of hoops (pinning threads, isolating cores, reassigning interrupts) to make sure you don't get descheduled. Because the scheduler won't know anything about priority inversions or even waiting threads, they all look runnable.