[ECOS] Thread activation disturbed by lower priority threads]

Alois Z. alois@gmx.at
Fri Aug 17 07:34:00 GMT 2007

> How many mutex's does your lower priority thread hold? From
> packages/kernel/current/src/sched/sched.cxx
> void Cyg_SchedThread::clear_inherited_priority()
> {
>     // A simple implementation of priority inheritance/ceiling
>     // protocols.  The simplification in this algorithm is that we do
>     // not reduce our priority until we have freed all mutexes
>     // claimed. Hence we can continue to run at an artificially high
>     // priority even when we should not.  However, since nested
>     // mutexes are rare, the thread we have inherited from is likely
>     // to be locking the same mutexes we are, and mutex claim periods
>     // should be very short, the performance difference between this
>     // and a more complex algorithm should be negligible. The most
>     // important advantage of this algorithm is that it is fast and
>     // deterministic.
> Does this explain what you see?
I should have always only one mutex claimed per thread. And always only for a very short period. What if several threads waiting for one mutex with priorities from 2 to 6 and the tread with priority 7 is holding the mutex. First of all will there be a reschedule after the mutex is realeased? 


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