On Sun, 24 Feb 2002, Matthew Dillon wrote:
> Bruce, your sys.dif was *invaluable*! It would have taken me a lot
> longer to figure out the interrupt disablement requirement around
> the icu_lock, and the statclock and hardclock forwarding issues (which I
> got working by the way!).
Thanks.
> It turns out that putting the pending masks in the per-cpu area was
> the right solution! It made statclock and hardclock forwarding easy
> (I can see why you didn't even try in your patch set, doing it with
> a global mask would be nearly impossible). In fact, it made everything
> unbelievably easy.
> ...
[This paragraph reordered]
> up. One of the best things about this patch set is that it is really
> flexible. We should be able to really make interrupts fly. In fact,
> it should even be possible for one cpu to steal another cpu's pending
> interrupt(s) fairly trivially, without having to resort to IPIs.
Good idea. Stealing would be even easier if the mask were global :-).
> The second issue is that cpu_switch() does not save/restore the
> PSL_I (interrupt disablement mask). I added a PSL word to the PCB
> structure to take care of the problem. Without this if you have
> a thread switch away while holding interrupts hard-disabled, the
> next thread will inherit the hard disablement. I saw the sti's
> you added in various places but I figured the best solution was
> to simply save/restore the state. The original code didn't have
cpu_switch() certainly needs to do this if it can be called with the
interrupt enable flag[s] in different states. I need the sti's (actually
enable_intr()'s because I don't want fast interrupts to be disabled
during context switches. This works because enabling interrupts is sure
to be safe, since we might be switching to a thread that will enable
them. Some sort of lock is needed to prevent interrupts interfering
with the switch. I think soft-masking them in critical_enter() is
sufficient in your version too.
Bruce
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