On Mon, 31 Dec 2007, M. Warner Losh wrote:
In message: <[EMAIL PROTECTED]>
John Baldwin <[EMAIL PROTECTED]> writes:
: The more correct fix though is to do a 'sched_prio()' at the start of the
: thread's main loop to set the priority and then not adjust it via msleep().
: Kernel threads really should never pass a priority to msleep() but always '0'
: (which means "don't change my priority").
Not PZERO? When should one use PZERO and when should one use a bare
'0'? Can this information be added to the man page?
PZERO is compatibility cruft which should never be used. Just a few
places in kern still use it to invent a priority when no suitable
priority (like PSOCK or PRIBIO) is already #defined. It isn't clear
where these invented priorities are suitable.
Otherwise, PZERO has a completely different meaning from either priority
0 (maximal) or the bare 0 arg to msleep. It means some middle priority,
or the bias from priority 0 to get to that middle priority, so that
after subtracting it, 0 becomes the middle priority. The bare 0 is
actualy priority 0 (maximal) overloaded to mean "don't change the
priority". This overloading doesn't lose anything except clarity since
nothing is permitted to wake up at maximal priority after a sleep.
(Maximal priority is reserved for realtime priority ithreads and even
much lower priority ithreads are not permitted to sleep, and non-interrupt
threads aren't permitted to run at ithread priorities except temporarily
for priority propagation.)
Bruce
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