Re: [Cbe-oss-dev] [PATCH]Add notification for active Cell SPU tasks

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Arnd Bergmann wrote:

On Wednesday 06 December 2006 23:04, Maynard Johnson wrote:
text(struct spu *spu, struct
spu_context *ctx)
Is this really the right strategy? First, it serializes all spu
context
switching at the node level.  Second, it performs 17 callouts for
I could be wrong, but I think if we moved the mutex_lock to be inside of the list_for_each_entry loop, we could have a race condition. For example, we obtain the next spu item from the spu_prio->active_mutex list, then wait on the mutex which is being held for the purpose of removing the very spu context we just obtained.


every context
switch. Can't oprofile internally derive the list of active spus
from the
context switch callout.
Arnd would certainly know the answer to this off the top of his head, but when I initially discussed the idea for this patch with him (probably a couple months ago or so), he didn't suggest a better alternative. Perhaps there is a way to do this with current SPUFS code. Arnd, any comments on this?


No code should ever need to look at other SPUs when performing an
operation on a given SPU, so we don't need to hold a global lock
during normal operation.

We have two cases that need to be handled:

- on each context unload and load (both for a full switch operation),
 call to the profiling code with a pointer to the current context
 and spu (context is NULL when unloading).

 If the new context is not know yet, scan its overlay table (expensive)
 and store information about it in an oprofile private object. Otherwise
 just point to the currently active object, this should be really cheap.

- When enabling oprofile initially, scan all contexts that are currently
 running on one of the SPUs. This is also expensive, but should happen
 before the measurement starts so it does not impact the resulting data.

Also, the notify_spus_active() callout is dependent on the return
code of
spu_switch_notify().  Should notification be hierarchical?  If I
only register
for the second one, should my notification be dependent on the
return code
of some non-related subsystem's handler.
I'm not exactly sure what you're saying here. Are you suggesting that a user may only be interested in acitve SPU notification and, therefore, shouldn't have to be depenent on the "standard" notification registration succeeding? There may be a case for adding a new registration function, I suppose; although, I'm not aware of any other users of the SPUFS notification mechanism besides OProfile and PDT, and we need notification of both active and future SPU tasks. But I would not object to a new function.


I think what Luke was trying to get to is that notify_spus_active() should
not call blocking_notifier_call_chain(), since it will notify other users
as well as the newly registered one. Instead, it can simply call the
notifier function directly.
Ah, yes. Thanks to both of you for pointing that out. I'll fix that and re-post.
-Maynard

	Arnd <><

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