Re: [patch] softirq-2.4.5-B0

[Ingo Molnar]

On Sun, 27 May 2001, David S. Miller wrote:

> Hooray, some sanity in this thread finally :-)

[ finally i had some sleep after a really long debugging session :-| ]

>  > 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 think we have no choice, unfortunately.

and i think function calls are not that scary anymore, especially not with
regparms and similar compiler optimizations. The function is simple, the
function just goes in and returns in 90% of the cases, which should be
handled nicely by most BTBs.

we have other fundamental primitives that are a function call too, eg.
dget(), and they are used just as frequently. In 2.4 we were moving
inlined code into functions in a number of cases, and it appeared to work
out well in most cases.

> 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 :-(

i believe the important thing is that the function has no serialization or
other 'heavy' stuff. BHs had the misdesign of not being restarted after
being re-enabled, and it caused performance problems - we should not
repeat history.

	Ingo