linux-kernel - Re: Lossy interrupts on x86

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Message-Id: <200709120929.52217.jbarnes@virtuousgeek.org>
Date:	Wed, 12 Sep 2007 09:29:52 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: Lossy interrupts on x86_64

On Wednesday, September 12, 2007, Randy Dunlap wrote:
> On Wed, 12 Sep 2007 08:33:15 -0700 Jesse Barnes wrote:
> > I just narrowed down a weird problem where I was losing more than
> > 50% of my vblank interrupts to what seems to be the hires timers
> > patch.  Stock 2.6.23-rc5 works fine, but the latest (171) kernel
> > from rawhide drops most of my interrupts unless I also have another
> > interrupt source running (e.g. if I hold down a key or move the
> > mouse I get the expected number of vblank interrupts, otherwise I
> > get between 3 and 30 instead of the expected 60 per second).
> >
> > Any ideas?  It seems like it might be bad APIC programming, but I
> > haven't gone through those mods to look for suspects...
>
> Also tickless?  (NO_HZ ?)
>
> I think I've seen some emails about tickless and keystrokes being
> needed to cause interrupts... but I'm not postive about it.
>
> but you said "any ideas"

Yeah, there's NO_HZ in the rawhide kernel too, but I'm getting timer
ticks normally afaict, it's just vblank interrupts that get lost...

/proc/interrupts on this machine (from NO_HZ, hires kernel):

[jbarnes@...rnes-t61 ~]$ cat /proc/interrupts
           CPU0       CPU1
  0:     290050     289541   IO-APIC-edge      timer
  1:       3862       3956   IO-APIC-edge      i8042
  8:          0          0   IO-APIC-edge      rtc0
  9:       1632       1643   IO-APIC-fasteoi   acpi
 12:     183662     183926   IO-APIC-edge      i8042
 14:      20626      20717   IO-APIC-edge      libata
 15:          0          0   IO-APIC-edge      libata
 16:      46812      46825   IO-APIC-fasteoi   yenta, uhci_hcd:usb3, i915@pci:0000:00:02.0
 17:      63715      63653   IO-APIC-fasteoi   uhci_hcd:usb4, HDA Intel, firewire_ohci, iwl4965
 18:          0          0   IO-APIC-fasteoi   uhci_hcd:usb5
 19:         52         36   IO-APIC-fasteoi   ehci_hcd:usb7
 20:         43         46   IO-APIC-fasteoi   uhci_hcd:usb1
 21:          0          0   IO-APIC-fasteoi   uhci_hcd:usb2
 22:          2          1   IO-APIC-fasteoi   ehci_hcd:usb6
2297:        937        944   PCI-MSI-edge      eth0
2298:      12392      12402   PCI-MSI-edge      ahci
NMI:          0          0
LOC:     290913     335027
ERR:          0


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