Ingo Molnar wrote:
>all that is needed now is some actual review of the new APIs from the
>conceptual angle (i've done that and i think they are okay, but more
>eyes see more), so that we make sure these are good and we wont need to
>discard any aspect of them anytime soon.
What about adding an u32 flags field to each one of the new futex
sys_calls. This gives you more freedom for future extensions without
changing the API again. Possible uses may be:
- Specify the futexes to be mm-local: By using the pair mm* and vaddr as
key it is possible to have process local futexes living on the same
hash with the following advantages:
1. no page_table lock contention (I implemented mm-local futexes
for my application after I noticed long latencies on SMP where a
high prio tasks spun in futex_wake while another task was doing
mmap/munmap on a second processor).
2. no vcache pollution (I guess 99% of all futexes will not be in
shared memory)
3. Slightly faster, since no page pinning is needed
- Specify queueing or unqueueing in priority order
Martin
P.S.
By the way, your latest futex patch still contains the bogus
if (!list_empty(&q.list)) conditional, that's always true since
you hold the locks at this point and no one can have removed us
from the list:
> add_wait_queue(&q.waiters, &wait);
> set_current_state(TASK_INTERRUPTIBLE);
>- if (!list_empty(&q.list))
>+ if (!list_empty(&q.list)) {
>+ unlock_futex_mm();
> time = schedule_timeout(time);
>+ }
Of course the test would be (and was) pretty necessary if you drop the
locks before the get_user(...) call. And I must admit that I still
can't see why you need to hold the locks across get_user. Even if it's
save to do so at least every automatic code checker will bark at this point.
-
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This archive was generated by hypermail 2b29 : Fri May 23 2003 - 22:00:48 EST