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

[Björn Steinbrink]

On 2006.06.26 05:05:14 +0200, Mike Galbraith wrote:
> On Mon, 2006-06-26 at 04:23 +0200, Mike Galbraith wrote:
> 
> > 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 didn't say that quite right.
> 
> The third case for my box is XT-PIC and your patch.  Previously, top
> showed the 10% interrupt load of a flood ping as all hi.  Now it's both
> hi and si when using XT-PIC, but it's no longer the 10% that agreed with
> the profile, it's  10% hi, but with an added ~7% si.

I see the following here, when a box is being ping flooded:

UP/SMP  stack-size  PIC-type  hi si
-----------------------------------
UP      8K          IO-APIC  0  16
UP      8K          XT-PIC   7  7
UP      4K          IO-APIC  0  16
UP      4K          XT-PIC   7  7

SMP     8K          IO-APIC  5  4 (forcedeth)
SMP     8K          IO-APIC  0  11 (tg3)

The UP system is a Thinkpad which only has a tg3 driven NIC. The SMP
system is x86_64, so there's no 4K stacks to test with, maybe I'll fetch
a i386 live CD to do some more valid tests on SMP.

The UP tests seem to show the IO-APIC hardirq are completely deferred
to be handled in a softirq, as the sum of "hi" and "si" with XT-PIC is
about equal to the "si" value with IO-APIC (the numbers are guessed
averages of the observed values, so the 2% difference is not too be
taken too serious).
The results for the forcedeth driven NIC do not agree though, and your
results differ from what I see as well, right? So I'm kinda lost again.

Björn
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