lkml.org 
[lkml]   [2006]   [Aug]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] cleanup and remove some extra spinlocks from rtmutex
    On 08/14, Esben Nielsen wrote:
    >
    > Well, we are talking about small optimizations now, moving only a few
    > instructions outside the lock. Except for one of them it is correct, but
    > it is worth risking stability for now?

    Yes, optimization is small, but I think this cleanups the code, which is (imho)
    more important. That said, I don't suggest this patch, it was a question. I stiil
    can't find a time to read the code hard and convince myself I can understand it :)

    Also, I think such a change opens the possibility for further cleanups.

    > >--- 2.6.18-rc3/kernel/rtmutex.c~2_rtm 2006-08-13 19:07:45.000000000 +0400
    > >+++ 2.6.18-rc3/kernel/rtmutex.c 2006-08-13 22:09:45.000000000 +0400
    > >@@ -236,6 +236,10 @@ static int rt_mutex_adjust_prio_chain(st
    > > goto out_unlock_pi;
    > > }
    > >
    > >+ /* Release the task */
    > >+ spin_unlock_irqrestore(&task->pi_lock, flags);
    > >+ put_task_struct(task);
    > >+
    >
    > So you want the task to go away here and use it below?

    task->pi_blocked_on != NULL, we hold task->pi_blocked_on->lock->wait_lock.
    Can it go away ?

    >
    > > top_waiter = rt_mutex_top_waiter(lock);
    > >
    > > /* Requeue the waiter */
    > >@@ -243,10 +247,6 @@ static int rt_mutex_adjust_prio_chain(st
    > > waiter->list_entry.prio = task->prio;
    > > plist_add(&waiter->list_entry, &lock->wait_list);
    > >
    > >- /* Release the task */
    > >- spin_unlock_irqrestore(&task->pi_lock, flags);
    > >- put_task_struct(task);
    > >-
    >
    > No! It is used in the line just above, so we better be sure it still
    > exists!

    See above. If I am wrong, we can move this line

    waiter->list_entry.prio = task->prio;

    up, under ->pi_lock. plist_del() doesn't need a valid ->prio.

    Thanks for your answer!

    Oleg.

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2006-08-15 08:43    [W:0.021 / U:60.772 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site