Thread (22 messages) 22 messages, 5 authors, 2015-10-08

Re: Next round: revised futex(2) man page for review

From: Peter Zijlstra <hidden>
Date: 2015-07-28 20:45:57
Also in: linux-api, lkml

On Tue, Jul 28, 2015 at 10:23:51PM +0200, Thomas Gleixner wrote:
quoted
       FUTEX_WAKE (since Linux 2.6.0)
              This  operation  wakes at most val of the waiters that are
              waiting (e.g., inside FUTEX_WAIT) on the futex word at the
              address  uaddr.  Most commonly, val is specified as either
              1 (wake up a single waiter) or INT_MAX (wake up all  wait‐
              ers).   No  guarantee  is provided about which waiters are
              awoken (e.g., a waiter with a higher  scheduling  priority
              is  not  guaranteed to be awoken in preference to a waiter
              with a lower priority).
That's only correct up to Linux 2.6.21.

Since 2.6.22 we have a priority ordered wakeup. For SCHED_OTHER
threads this takes the nice level into account. Threads with the same
priority are woken in FIFO order.
Maybe don't mention the effects of SCHED_OTHER, order by nice value is
'wrong'.

Also, this code seems to use plist, which means it won't do the right
thing for SCHED_DEADLINE either.

Do we want to go fix that?
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