Re: [RFC PATCH for 4.18 00/14] Restartable Sequences

On Wed, May 02, 2018 at 03:53:47AM +0000, Daniel Colascione wrote:

The usual approach to "better" is an "adaptive mutex". Such a thing, when
it attempts to acquire a lock another thread owns, spins for some number of
iterations, then falls back to futex. I guess that's a little better than
immediately jumping to futex, but it's not optimal. We can still spin when
the lock owner isn't scheduled, and the spin count is usually some guess
(either specified manually or estimated statistically) that's not
guaranteed to produce decent results. Even if we do pick a good spin count,
we run a very good chance of under- or over-spinning on any given
lock-acquire. We always want to sleep when spinning would be pointless.

Look for the FUTEX_LOCK patches from Waiman.