NetBSD Problem Report #55497

From  Sun Jul 19 01:23:16 2020
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Date: Sat, 18 Jul 2020 17:07:30 -0700 (PDT)
Subject: piixide causing interrupt storm
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>Number:         55497
>Category:       port-amd64
>Synopsis:       piixide causing interrupt storm
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jul 19 01:25:00 +0000 2020
>Release:        NetBSD 7.2_STABLE
  Aaron J. Grier | "Not your ordinary poofy goof." |
  "The price of reliability is the pursuit of the utmost simplicity.  It
   is a price which the very rich find most hard to pay."  -- Tony Hoare

System: NetBSD 7.2_STABLE NetBSD 7.2_STABLE (GENERIC) #1: Sun Feb 10 18:29:20 PST 2019 amd64
Architecture: x86_64
Machine: amd64
seeing interrupt storm on ioapic0 pin 18:

ioapic0 pin 18                         800784898423   222444

eating roughly half a core with interrupt time.  why?
boot system, examine output of vmstat -i.

disable interrupts by setting bit10 (disable interrupts) of PCI control
register on unused piixide0 interface:

piixide0 at pci0 dev 31 function 1: Intel 82801GB/GR IDE Controller (ICH7) (rev.  0x01)
piixide0: bus-master DMA support present
piixide0: primary channel configured to native-PCI mode
piixide0: using ioapic0 pin 18 for native-PCI interrupt
atabus0 at piixide0 channel 0
piixide0: secondary channel configured to native-PCI mode
piixide0: secondary channel ignored (disabled)
# nothing connected to atabus0!

faramir$ sudo pcictl /dev/pci0 read -b 0 -d 31 -f 1 4
faramir$ sudo pcictl /dev/pci0 write -b 0 -d 31 -f 1 4 0x02880405
# interrupt storm stops.

I have not tried a newer kernel yet, but have observed this since


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