Re: mutexes, IPL, tty locking

[David Holland <dholland-tech%netbsd.org@localhost>]

On Tue, Jan 26, 2010 at 10:39:23AM +0000, Andrew Doran wrote:
 > > I'm not sure it's as rare as all that; it just mostly doesn't overtly
 > > fail. Instead you end up silently running at a higher IPL than
 > > necessary, and that buys you longer interrupt latencies and more
 > > dropped packets and all that.
 > 
 > I have done extensive testing to on SPL behaviour and can confidently say
 > that with our current setup it simply does not matter unless you have a
 > very poorly written bit of code - in which case that's your problem, not
 > the interrupt masking system.

Sure, but the real question is how many such poorly written bits of
code currently exist and how hard they are to find and fix.

If what you mean to say is that you've specifically gone and looked
for such cases and not found any, then great. But so far nobody's been
willing to stick their neck out to make this assertion -- only the
weaker one "if such code exists, it's wrong."

-- 
David A. Holland
dholland%netbsd.org@localhost