Re: [PATCH] i386: Fix softirq accounting with 4K stacks

[Mike Galbraith]

On Sun, 2006-06-25 at 20:42 +0200, BjÃrn Steinbrink wrote:
> I just booted with both patches applied, mine and Mike's, and that
> actually makes a difference in hardirq cpu time accounting. With my
> patch only, hi is 0 in top while the box gets a ping flood. With both
> patches, I get about 1% hi. Mike's patch causes update_process_times()
> to be called twice on UP, but that alone shouldn't change the
> percentages, right?

Yes, you definitely need to comment out the other call if you test the
SMP path on UP+IO-APIC.

> OTOH top shows "hi" as zero with 8K stacks as well unless Mike's patch
> is applied, so the results with Mike's patch are bogus (if so, why?) or
> hardirq accounting is broken in general.

Something is certainly still b0rken.  I still get three different
answers to the question "what is my cpu usage" depending on
configuration.  With stock UP kernel with no IO-APIC, interrupt load is
all hi.  With your patch and IO-APIC, it's all si.  SMP shows a mix of
both.

I like the result of using the SMP path if you have an IO-APIC best,
though I haven't verified them against a profile for accuracy.  Taking a
peek at the profile confirms that it is indeed mixed, so anything
showing the load as being either hi or si has to be wrong.

	-Mike

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