general config preemption Q: preempt-model and Big-Lock Preemption

[Linda Walsh]

A question that comes to mind every time I go through the settings
for "Preemption Model" and "Preempt The Big Kernel Lock".

Do each of the combinations "make sense", or are some "no-ops"?
For model, we have 1) no forced (server), 2) Voluntary (Desktop)
3) preemptible (low-latency Desktop), and for Big Lock Preemption (BLP),
we have "yes" or "no".

Questions:

1) What is the difference between "no forced" and "voluntary"?  Doesn't
 voluntary normally mean "not forced"?

2) If a process is not preemptible, then it seems this would be "doubly
 so" in the kernel when the big-lock is held.  So does the big-lock
 preemption question have any effect (when preempt-model="no forced").

3) If a process is "fully preemptible" but "BLP=false", is that
 much different than "voluntary preemption" & BLP=false?  I.e. --
 should 'preemptible kernel' also imply "BLP=true"...i.e.

_Should_ (would?) the following change be "somewhat" identical to
current config options:

 O1) "Preempt Model"="no-forced preemption" (would set
 preempt-big-kern-lock to FALSE and doesn't display that question).

 O2) "Voluntary Preemption" (presuming there are voluntary preemption
 points in the kernel in places where the big-K-lock is held), then
 configuration would still ask whether to  "Preempt The Big Kernel Lock".

 O3) "Preemptible model"="allow-kernel-preemption" (would set
 preempt-big-kern-lock to TRUE and doesn't display that question).


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/