Gilles Chanteperdrix wrote:
> On Jan 23, 2008 7:34 PM, Philippe Gerum <[EMAIL PROTECTED]> wrote:
>> Gilles Chanteperdrix wrote:
>>> On Jan 23, 2008 6:48 PM, Philippe Gerum <[EMAIL PROTECTED]> wrote:
>>>> Gilles Chanteperdrix wrote:
>>>>> Gilles Chanteperdrix wrote:
>>>>>  > Please find attached a patch implementing these ideas. This adds some
>>>>>  > clutter, which I would be happy to reduce. Better ideas are welcome.
>>>>>  >
>>>>> Ok. New version of the patch, this time split in two parts, should
>>>>> hopefully make it more readable.
>>>> Ack. I'd suggest the following:
>>>> - let's have a rate limiter when walking the zombie queue in
>>>> __xnpod_finalize_zombies. We hold the superlock here, and what the patch
>>>> also introduces is the potential for flushing more than a single TCB at
>>>> a time, which might not always be a cheap operation, depending on which
>>>> cra^H^Hode runs on behalf of the deletion hooks for instance. We may
>>>> take for granted that no sane code would continuously create more
>>>> threads than we would be able to finalize in a given time frame anyway.
>>> The maximum number of zombies in the queue is
>>> 1 + XNARCH_WANT_UNLOCKED_CTXSW, since a zombie is added to the queue
>>> only if a deleted thread is xnpod_current_thread(), or if the XNLOCKSW
>>> bit is armed.
>> Ack. rate_limit = 1? I'm really reluctant to increase the WCET here,
>> thread deletion isn't cheap already.
> I am not sure that holding the nklock while we run the thread deletion
> hooks is really needed.

Deletion hooks may currently rely on the following assumptions when running:

- rescheduling is locked
- nklock is held, interrupts are off
- they run on behalf of the deletor context

The self-delete refactoring currently kills #3 because we now run the
hooks after the context switch, and would also kill #2 if we did not
hold the nklock (btw, enabling the nucleus debug while running with this
patch should raise an abort, from xnshadow_unmap, due to the second

It should be possible to get rid of #3 for xnshadow_unmap (serious
testing needed here), but we would have to grab the nklock from this
routine anyway.


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