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xen-devel
Re: [Xen-devel] pv_ops dom0 clock only runs under load
On Thu, 05 Mar 2009 21:41:44 -0800
Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> Milan Holzäpfel wrote:
>
> > The clock only seems to run if the system is under load (e.g. run
> > "while true; do echo -n; done" in a shell).
> > With the CPU loaded and the clock running everything seems to work
> > quite well (hard disk and network access, that is.)
> >
> > Changing the "xen" clocksource to "tsc" via sysfs didn't make a
> > difference. Enabling or disabling the "tickless" option doesn't make a
> > difference either.
> >
>
> That's pretty mysterious; it does suggest your cpu's tsc is not ticking.
Excerpt from the dmesg (2.6.29 pvops with / without Xen)
[ 4.870697] Marking TSC unstable due to TSC halts in idle
Saw it scrolling by
> Some questions:
>
> 1. does it work OK with 2.6.18 or other dom0 kernels?
Yes. 2.6.18.8 from the hg repo works fine.
> 2. what clocksource does the kernel choose when you boot native?
hpet (both 2.6.29 without Xen and 2.6.18 without Xen)
> 3. what does /proc/cpuinfo contain?
Under 2.6.29/Xen:
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.73GHz
stepping : 8
cpu MHz : 1729.018
cache size : 2048 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu de tsc msr pae cx8 apic mtrr cmov clflush acpi mmx fxsr
sse sse2 ss up est hypervisor
bogomips : 3458.03
clflush size : 64
power management:
> 4. what does /proc/interrupts contain?
Under 2.6.29/Xen:
CPU0
1: 361 xen-pirq-pirq i8042
8: 0 xen-pirq-pirq rtc0
9: 148 xen-pirq-pirq acpi
12: 9 xen-pirq-pirq i8042
14: 28 xen-pirq-pirq ata_piix
15: 0 xen-pirq-pirq ata_piix
22: 2230 xen-pirq-pirq eth0
24: 9300 xen-dyn-virq timer0
25: 0 xen-dyn-ipi spinlock0
26: 0 xen-dyn-ipi resched0
27: 0 xen-dyn-ipi callfunc0
28: 0 xen-dyn-virq debug0
29: 0 xen-dyn-ipi callfuncsingle0
30: 0 xen-dyn-event xenbus
NMI: 0 Non-maskable interrupts
LOC: 0 Local timer interrupts
CNT: 0 Performance counter interrupts
RES: 0 Rescheduling interrupts
CAL: 0 Function call interrupts
TLB: 0 TLB shootdowns
SPU: 0 Spurious interrupts
ERR: 0
MIS: 0
> 5. are there any power management options in the bios you could try
> turning on/off?
I turned both "Intel SpeedStep" and "CPU Power Saving Mode" off, but it
didn't change anything (2.6.29 with / without Xen)
> > Output is from netconsole, so some messages might have got lost. I
> > piped the output through "sort".
> >
> Why?
Initially I thought packets had got reordered because the indicated
time jumped backwards in one place. (UDP packets travelling across a
router and WiFi connectiion). I replaced the connection with direct
ethernet, and saw that indeed no reordering hat taken place. Packet
loss shouldn't be an issue now too.
By the way, I booted the 2.6.29 pvops enabled kernel without Xen and
the tsc timesource only increments when the CPU was loaded, too. On
2.6.18 (without Xen) it worked normally (also with the BIOS options
enabled).
Also, the jiffies timesource seems somewhat broken. Setting it under
the 2.6.29 pvops kernel without Xen made the clock stop completely
(also when under load). It couldn't be changed back to hpet anymore.
I will try whether disabling kernel stuff (there is something called
"cpuidle" compiled in) makes the tsc clocksource work again.
Let me know if you need further information etc. and thanks for your
support.
Regards,
Milan
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