[Bug nptl/16410] pthread_cond_timedwait has 70us latency when abstime already expired

["triegel at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16410

Torvald Riegel <triegel at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |triegel at redhat dot com
         Resolution|---                         |WONTFIX

--- Comment #3 from Torvald Riegel <triegel at redhat dot com> ---
I do not think that pthread_cond_timedwait is meant to be used with absolute
timeouts that have already expired.  The intent is to actually wait for a
condition.  If timeouts are extremely short (or expired), then the typical
usage pattern of a pthread_cond_timedwait essentially becomes busy-waiting by
constantly acquiring and releasing the associated mutex.  This is not what
condition variables are intended for.

Adding the clock_gettime call as a check can reduce wake-up latency in other
scenarios (by the amount of time required to perform the clock_gettime call);
thus, the proposed change would not be a clear performance win generally.

Also, if programs have extremely short or potentially expired timeouts, they
can easily run clock_gettime themselves in the critical section before calling
pthread_cond_timedwait.

Thus, I'm closing this as WONTFIX.

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