linux-kernel - Re: [PATCH] x86-64 highres/dyntick support

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Message-Id: <200705140217.11515.s0348365@sms.ed.ac.uk>
Date:	Mon, 14 May 2007 02:17:11 +0100
From:	Alistair John Strachan <s0348365@....ed.ac.uk>
To:	tglx@...utronix.de
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	john stultz <johnstul@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	Chris Wright <chrisw@...s-sol.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86-64 highres/dyntick support

On Sunday 06 May 2007 21:58:47 Thomas Gleixner wrote:
> I'm pleased to announce the first cut of the final x86_64
> highres/dyntick support, which I did based on Chris Wright's patch set,
> which is again based on Arjan van de Ven's initial work:

I've noticed a few problems with this patch series, which I manually (without 
difficulty) ported to 2.6.22-rc1.

Firstly, the output of /proc/interrupts looks a bit strange. NO_HZ isn't 
enabled, just high resolution timers. HZ was set to 1000.

alistair@...ocles:~$ cat /proc/interrupts
           CPU0       CPU1
  0:        195          0   IO-APIC-edge      timer
  1:         21      13698   IO-APIC-edge      i8042
  8:          0          0   IO-APIC-edge      rtc
  9:          0          0   IO-APIC-fasteoi   acpi
 14:        117      51178   IO-APIC-edge      libata
 15:          0          0   IO-APIC-edge      libata
 18:        455     449373   IO-APIC-fasteoi   lan-sky, EMU10K1
 19:          0          3   IO-APIC-fasteoi   yenta, ohci1394
 20:        220      86188   IO-APIC-fasteoi   ohci_hcd:usb2
 21:          0         26   IO-APIC-fasteoi   ehci_hcd:usb1
 22:          0        273   IO-APIC-fasteoi   sata_nv
 23:        928     507781   IO-APIC-fasteoi   sata_nv, lan
NMI:          0          0
LOC:    4723272    4797930
ERR:          0

Only 195 timer interrupts? I only see this on an AMD Opteron, it doesn't occur 
on an Intel Core 2 Duo. Mainline reports this counter regularly increasing 
with or without the acpi_pm clocksource loaded.

Secondly, /proc/cpuinfo seems to be broken:

alistair@...ocles:~$ cat /proc/cpuinfo | grep MHz
cpu MHz         : 210779.550
cpu MHz         : 210779.550

Unless my CPU is just under 80 times faster than it used to be, these numbers 
are incorrect. I expect 2700.50, or something similar. cpufreq isn't compiled 
in.

Finally, and possibly related, the dmesg timestamps seem to be totally broken. 
Apparently my machine booted in less than 1 second, with the last messages 
as:

[    0.607862] bridge: topology change detected, propagating
[    0.607862] bridge: port 2(lan-sky) entering forwarding state
[    0.830472] Linux agpgart interface v0.102 (c) Dave Jones

Of course, all of these problems might be PEBKAC, but I'm sceptical.

Find the kernel config, updated patch (for 2.6.22-rc1), dmesg, contents 
of /proc/interrupts and /proc/cpuinfo here:

http://devzero.co.uk/~alistair/2.6.22-rc1-hrt/

-- 
Cheers,
Alistair.

Final year Computer Science undergraduate.
1F2 55 South Clerk Street, Edinburgh, UK.
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