On Thu, 14 Jun 2007, Andrew Doran wrote:
> I'm not yet sure what we need to set into SR in this
case, but post
> yamt-idlelwp, LWPs should start up at IPL_SCHED as far
as MD code is
> concerned. cpu_switchto() is expected to maintain the
IPL at IPL_SCHED or
> above across the switch. If I read the code correctly,
PSL_LOWIPL enables
> all interrupts.
Ah - I just looked at the alpha changes, and the code to
set the IPL
level for the new lwp was removed, leaving it what was
copied from the
parent. I thought I had found something simllar in the i386
code, but
I can't find what I remember.
> The call into lwp_startup() does an spl0(). Before it
does that, it also
> unlocks the previous LWP if any. If we enable
interrupts before unlocking
> the previous LWP, we can end up taking an interrupt and
trying to acquire
> a spinlock that is already held.
In that case, I think not changing the interrupt masking
when forking a
new lwp is probably what is now desired. The new process
will inherit the
IPL level from the parent process (although I'm now sure
what it actually
is for the various ports).
--
Michael L. Hitch mhitch montana.edu
Computer Consultant
Information Technology Center
Montana State University Bozeman, MT USA
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