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SubjectRe: Today Linus redesigns the networking driver interface (was Re: tulip driver in ...)
Keith Owens writes:
> On Tue, 22 Sep 1998 17:27:36 +1000,
> Richard Gooch <rgooch@atnf.csiro.au> wrote:
> >So a heuristic to avoid BH processing isn't really worthwhile, I now
> >think, nor is a return flag from interrupt handlers saying "please
> >don't process BH's now", since the (bh_active & bh_mask) test is good
> >enough.
> >The simple rule: "if you haven't registered/marked active a BH, then
> >you aren't going to trigger BH processing, so don't worry about it"
> >seems like the right thing.
>
> Something that has been puzzling me about all of this selective do
> or don't mark_bh(). If there is data to be processed then the BH
> must be run eventually. When does the interrupt handler finally
> decide to mark_bh()? The obvious way is on a later interrupt but
> what happens if no more interrupts arrive? Extremely unlikely but
> possible.

You'll get another interrupt 10 ms later at worst. You'll also run
BH's on return from syscall, IIRC.

Besides, it seems to me that the argument has been over not processing
BH's in after running an interrupt handler *which won't register/mark
active a BH in the first place*. The so-called "fast interrupts" that
people still seem to believe in.

> The only other way to mark_bh() is something external to the interrupt
> handler, say a timer. But that just complicates the code - is it worth
> it? Does it really cost that much to run the BH mask?

I can't imagine so. It's only a few more cycles.

Regards,

Richard....

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