Extended periods of "waking up thread %d on cap %d"

[Ben Gamari]

Simon Marlow <marlowsd at gmail.com> writes:

> So I think we could adopt a similar policy for STM.  The mutex is 
> lockTSO()/unlockTSO(), which is already taken in STM.c:unpark_tso().  To 
> indicate that a thread has already been sent a wakeup message, we could 
> set tso->block_info.closure to a special value - normally it would be 
> END_TSO_QUEUE for a thread blocked in STM.  I've been peering at the 
> code a bit, and I'm pretty sure this is safe and doesn't involve many 
> changes to the RTS.
>
> Do you want to try this out and let me know if you get stuck?
>
Here[1] is a first stab at this. I'm currently waiting for a testsuite
run to finish but the patch at very least doesn't seem to break
anything obvious. Moreover, the number of wake-ups sent in my benchmark
appears to be much more reasonable now. Let me know if there's anything
obviously wrong here.

Cheers,

- Ben


[1] https://github.com/bgamari/ghc/commits/stm-mutex