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SubjectRe: [3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interrupt responses)
On Thu, 14 Mar 2013, Alan Stern wrote:

> > > Can you try to do a git bisect for this? Is the sluggish system
> > > response clear enough that you can tell reliably when it is present and
> > > when it isn't?
> >
> > That was my first thought, but unfortunately I am afraid there will be
> > point at which I will easily make a bisection mistake, as the
> > responsiveness of the system varies over time, so it's not really a
> > 100% objective measure.
>
> All right.
>
> There have been only three significant changes to uhci-hcd since last
> summer, and two of them appear to be completely unrelated to this
> issue. The three commits are
>
> 3171fcabb169 USB: uhci: beautify source code
> 13996ca7afd5 USB: uhci: check buffer length to avoid memory
> overflow
> 0f815a0a700b USB: UHCI: fix IRQ race during initialization
>
> Reverting the first two almost certainly will not have any effect, but
> you may as well try it anyway. The third commit may be relevant.

I have reverted all three commits, and the "nobody cared" is still there.

> If you revert all three and still see the problem then it must be
> caused by changes outside of the USB stack. Differences in interrupt
> routing could be a result of changes to PCI or ACPI. Have you compared
> the current /proc/interrupts with versions from earlier kernels without
> this problem?

The diff of stripped-down (without CPU statistics) /proc/interrupts from
some oldish working 3.1 and the current tree:

--- /tmp/interrupts-old.txt 2013-03-14 16:30:46.938710286 +0100
+++ /tmp/interrupts-new.txt 2013-03-14 16:30:18.954571413 +0100
@@ -3,27 +3,28 @@
8:IO-APIC-edge rtc0
9:IO-APIC-fasteoi acpi
12:IO-APIC-edge i8042
- 16:IO-APIC-fasteoi uhci_hcd:usb6
- 17:IO-APIC-fasteoi uhci_hcd:usb7
- 18:IO-APIC-fasteoi ata_generic, uhci_hcd:usb8
- 19:IO-APIC-fasteoi ehci_hcd:usb2
- 20:IO-APIC-fasteoi uhci_hcd:usb3
- 21:IO-APIC-fasteoi uhci_hcd:usb4
- 22:IO-APIC-fasteoi uhci_hcd:usb5
- 23:IO-APIC-fasteoi ehci_hcd:usb1
+ 16:IO-APIC-fasteoi uhci_hcd:usb4
+ 17:IO-APIC-fasteoi uhci_hcd:usb5
+ 18:IO-APIC-fasteoi ata_generic, uhci_hcd:usb6
+ 19:IO-APIC-fasteoi ehci_hcd:usb8
+ 20:IO-APIC-fasteoi uhci_hcd:usb1
+ 21:IO-APIC-fasteoi uhci_hcd:usb2
+ 22:IO-APIC-fasteoi uhci_hcd:usb3
+ 23:IO-APIC-fasteoi ehci_hcd:usb7, i801_smbus
40:PCI-MSI-edge PCIe PME
41:PCI-MSI-edge PCIe PME
42:PCI-MSI-edge PCIe PME
43:PCI-MSI-edge ahci
44:PCI-MSI-edge i915
45:PCI-MSI-edge eth0
- 46:PCI-MSI-edge iwlagn
+ 46:PCI-MSI-edge iwlwifi
47:PCI-MSI-edge snd_hda_intel
NMI:Non-maskable interrupts
LOC:Local timer interrupts
SPU:Spurious interrupts
PMI:Performance monitoring interrupts
IWI:IRQ work interrupts
+RTR:APIC ICR read retries
RES:Rescheduling interrupts
CAL:Function call interrupts
TLB:TLB shootdowns
IRQ16 is routed differently (usb4 vs usb6), so that might be relevant.

> Is occurrence of the "nobody cared" connected with any particular
> device? Somebody reported a similar problem not long ago (although IIRC
> it was for OHCI rather than UHCI) which appeared to be related to
> activity on the built-in webcam.

Will check this. No external devices are plugged in, I think the only
internal one it has is bluetooth chip. I'll try turning it off.

--
Jiri Kosina
SUSE Labs


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