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List:       openbsd-bugs
Subject:    Re: Interrupts hover above 40% when idle on Dell Latitude E7450
From:       Scott Cheloha <scottcheloha () gmail ! com>
Date:       2022-01-31 17:24:55
Message-ID: 20220131172455.dm2xthnvxn72gei4 () jetsam ! attlocal ! net
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On Sun, Jan 30, 2022 at 10:41:34AM -0500, Ryan Kavanagh wrote:
> On Sun, Jan 30, 2022 at 12:39:02AM -0600, Scott Cheloha wrote:
> > > btrace -e 'profile:hz:100 { @[kstack] = count(); }' > /tmp/btrace.out
> > > 
> > > for ten seconds and ran the output through
> > > 
> > > https://github.com/brendangregg/FlameGraph/raw/master/stackcollapse-bpftrace.pl
> > > https://github.com/brendangregg/FlameGraph/raw/master/flamegraph.pl
> > > 
> > > The output of stackcollapse-bpftrace.pl and flamegraph.pl are attached
> > > as btrace.collapsed and btrace.svg.
> > 
> > The flamegraph suggests that you spent 10% of that time servicing
> > ichiic(4) interrupts from idle.
> > 
> > That could be a fluke though.
> 
> In case it was a fluke, I've regenerated the flamegraph on 7.0
> GENERIC.MP#293 amd64 using 10 seconds of output on an idle machine.
> Please see attached.
> 
> > What does the main systat view look like in the interrupt column?
> > 
> > $ systat 1
> 
> Again on #293:
> 
> Interrupts    (range after idling for a few seconds)
>  247 total    (235-260)
>  200 clock    (200-200)
>   21 ipi      (16-23)
>    1 acpi0    (0-1)
>    6 inteldrm (5-7)
>      azalia1  (0-0)
>   11 iwm0     (10-16)
>      ehci0    (0-0)
>    1 ahci0    (0-1)
>    1 ichiic0  (0-1)
>    6 pckbc0   (0-0)
>      pckbc0   (0-0)

Based on these numbers and the similar-looking flamegraph I'd say
you're spending a relatively large amount of time handling ichiic(4)
interrupts.

I don't know anything about that device but my guess is that it is
slow if you're spending that much time in x86_bus_space_io_read_1()
and its _write_1() counterpart.

Someone else is going to have to weigh in on what might be the cause
and solution.

Thank you providing the traces.

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