[PATCH] D36607: [Support/Parallel] - Do not spawn thread for single/last task.

[George Rimar via Phabricator via llvm-commits]

grimar added a comment.

In https://reviews.llvm.org/D36607#843164, @davide wrote:

> Adaptive mutexes (e.g. for pthread_*) work using this principle. The kernel maintains a shared page and threads contending on the lock spin until the lock owner isn't descheduled.
>  This works because in general the cost of a context switch overcomes that of wasting few cycles spinning (under the assumption the CS is small).
>  An approximation of this scheme would be that of spinning for a certain number of cycles decreasing a variable each time (and going to sleep when the variable reaches zero).
>  This is, FWIW, what FreeBSD pthread mutexes do.
>  A different (and possibly more effective) proposal for `Parallel` would be that of exploring work-stealing algorithms for queueing.


Interesting.
And what this patch do is orthogonal thing, since helps to avoid all threading/syncing overhead at all for free in some cases.


https://reviews.llvm.org/D36607