Re: NPTL mutex and the scheduling priority

Atsushi Nemoto
2006-09-07T09:30:31Z

On Thu, 7 Sep 2006 04:32:44 -0400, Jakub Jelinek <jakub@redhat.com> wrote:
> > But pthread_cond_signal and sem_post still wakeup a thread in FIFO
> > order, as you can guess.
> >
> > With the plist patch (applied by hand), I can get desired behavior.
> > Thank you. But It seems the patch lacks reordering on priority
> > changes.
>
> Yes, either something like the plist patch for FUTEX_WAKE etc. or, if that
> proves to be too slow for the usual case (non-RT threads), FIFO wakeup
> initially and conversion to plist wakeup whenever first waiter with realtime
> priority is added, is still needed. That will cure e.g. non-PI
> pthread_mutex_unlock and sem_post. For pthread_cond_{signal,broadcast} we
> need further kernel changes, so that the condvar's internal lock can be
> always a PI lock.

Thank you, I'll stay tuned.

> > <off_topic>
> > BTW, If I tried to create a PI mutex on a kernel without PI futex
> > support, pthread_mutexattr_setprotocol(PTHREAD_PRIO_INHERIT) returned
> > 0 and pthread_mutex_init() returned ENOTSUP. This is not a right
> > behavior according to the manual ...
> > </off_topic>
>
> Why?
> POSIX doesn't forbid ENOTSUP in pthread_mutex_init to my knowledge.

http://www.opengroup.org/onlinepubs/009695399/functions/pthread_mutexattr_setprotocol.html
http://www.opengroup.org/onlinepubs/009695399/functions/pthread_mutex_init.html

>From ERRORS section of pthread_mutexattr_setprotocol:

The pthread_mutexattr_setprotocol() function shall fail if:
[ENOTSUP]
The value specified by protocol is an unsupported value.

And ENOTSUP is not enumerated in ERRORS section of pthread_mutex_init.

---
Atsushi Nemoto