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SubjectRe: 2.2.x run_bottom_halves bug
   Date: 	Thu, 6 May 1999 15:28:04 -0400 (EDT)
From: "Benjamin C.R. LaHaise" <blah@kvack.org>

I've been testing drivers ported from 2.0 to 2.2 and I'm noticing
that bottom halves are occasionally getting delayed until the next
interrupt, which usually turns out to be the timer going off,
adding an unnecessary 10-20ms delay. The case I've encountered
this with is when a bottom half handler triggers another bottom
half in my driver's packet reassemble code.

This was under discussion recently, and you simply cannot safely do
what your patch is trying to do.

For example, when should your loop exit? How do you handle starvation
cases (watch what a few parallel ping floods do to the machine over
100baseT with your change applied). You will pin the cpu in BH
processing. If the cpu is slow enough, or it has enough work to do
over and over, it may never come out. See?

The consensus is that most of us do agree that we do want to relook at
the bits again for several cases, but certainly not endlessly.

You have to put some kind of heuristic cork into the scheme or else
you end up with huge problems.

Later,
David S. Miller
davem@redhat.com

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