Re: [PATCH v4 00/15] Add futex2 syscalls

Às 01:51 de 04/06/21, Zebediah Figura escreveu:

On 6/3/21 2:59 PM, André Almeida wrote:

quoted

  ** The wait on multiple problem

  The use case lies in the Wine implementation of the Windows NT
interface
  WaitMultipleObjects. This Windows API function allows a thread to sleep
  waiting on the first of a set of event sources (mutexes, timers,
signal,
  console input, etc) to signal.  Considering this is a primitive
  synchronization operation for Windows applications, being able to
quickly
  signal events on the producer side, and quickly go to sleep on the
  consumer side is essential for good performance of those running
over Wine.

I know this is part of the cover letter, but I really do want to clarify
that this isn't really accurate. The use case that this is referring to
is not "the Wine implementation of WaitForMultipleObjects", it is an
out-of-tree implementation of WaitForMultipleObjects that provides
improved performance compared to the in-tree implementation.

This is especially salient because:

(1) this out-of-tree implementation is only in a small handful of cases
any more performant than a different out-of-tree implementation which
uses eventfd and poll() instead;

(2) these implementations will remain out-of-tree due to compatibility
and robustness problems;

(3) I believe there is potential for an upstreamable implementation
which does not rely on futex or futex2.

I'll let it more clear next time that this applies to Proton's Wine, and
not Wine.

Along with that, wait on multiple will be useful for other workloads,
such as the ones that uses Boost's mass locking algorithms and native
game engines for instance.