Re: [patch] softirq-2.4.5-B0

["David S. Miller" <davem@redhat.com>]

Ingo Molnar writes:
 > the bug/misbehavior causing bad latencies turned out to be the following:
 > if a hardirq triggers a softirq, but syscall-level code on the same CPU
 > disabled local bhs via local_bh_disable(), then we 'miss' the execution of
 > the softirq, until the next IRQ. (or next direct call to do_softirq()).

Hooray, some sanity in this thread finally :-)

Yes, this makes perfect sense, this is indeed what can happen.

 > the attached softirq-2.4.5-B0 patch fixes this problem by calling
 > do_softirq()  from local_bh_enable() [if the bh count is 0, to avoid
 > recursion].

Yikes!  I do not like this fix.

I'd rather local_bh_enable() not become a more heavy primitive.

I know, in one respect it makes sense because it parallels how
hardware interrupts work, but not this thing is a function call
instead of a counter bump :-(

Any other ideas how to zap this?

Later,
David S. Miller
davem@redhat.com