lkml.org 
[lkml]   [2011]   [Jan]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC][RT][PATCH 3/4] rtmutex: Revert Optimize rt lock wakeup
From
Date
On Mon, 2011-01-03 at 15:22 -0500, Steven Rostedt wrote:
> On Mon, 2011-01-03 at 14:06 -0500, Steven Rostedt wrote:
>
> >
> > if (adaptive_wait(&waiter, orig_owner))
> > sleep = 1;
> > else
> > sleep = 0;
> >
> > if (sleep)
>
>
> > raw_spin_lock(&lock->wait_lock);
> > saved_state = rt_set_current_block_state(saved_state);
> > if (!lock->owner && &waiter == rt_mutex_top_waiter(lock))
> > sleep = 0;
> > raw_spin_unlock(&lock->wait_lock);
>
> I may be able to remove the above locks and replace it with:
>
> saved_state = rt_set_current_blocked_state(saved_state);
> if (orig_owner == rt_mutex_owner(lock))
> schedule_rt_mutex(lock);
>
> -- Steve

Isn't it possible to miss a wakeup here if the waiter becomes preempted?

Recall that adaptive wait is a preemptive wait. Hence the (I believe)
original reason we did the adaptive spin in a (transitioning) sleep
state.

-PWM

>
>
> > if (sleep)
> > schedule_rt_mutex(lock);
> > saved_state = rt_restore_current_blocked_state(saved_state);
> > }
> >
> > Otherwise we can risk the wakeup_next_waiter() missing the wakeup.
> >
> > To clarify, we want the adaptive_wait() to run as TASK_RUNNING. Then if
> > we must sleep, then we must set the state to TASK_UNINTERRUPTIBLE, test
> > again if we can still the lock, and if not then sleep. Otherwise, if a
> > wakeup happens just before we set the state to TASK_UNINTERRUPTIBLE,
> > then we miss the wake up all together.
> >
> > I can do this change, and see what impact it makes.
> >
> > I'm also curious if this ever worked? If it did not, then are you sure
> > your tests that show the benefit of it was true. I don't have a large
> > scale box at my disposal ATM, so I can only see what this does on 4way
> > machines.
> >
> > -- Steve
> >
>
>




\
 
 \ /
  Last update: 2011-01-05 00:55    [from the cache]
©2003-2011 Jasper Spaans