Re: pinning, tsc and apic

[Anthony Liguori <anthony@codemonkey.ws>]

Marcelo Tosatti wrote:
> On Mon, May 12, 2008 at 02:19:24PM -0500, Ryan Harper wrote:
>   
> Hi Ryan,
>
> There are two places that attempt to use delivery mode 7: kexec crash
> and io_apic_64.c::check_timer().
>
> The later will happen if the guest fails to receive PIT IRQ's for 10
> ticks. If you're using HZ=1000 thats 10ms. See timer_irq_works().
>
> The in-kernel pit emulation has logic which avoids injecting more than
> one IRQ during 10ms.
>
> Note that the guest 10ms delay is TSC based and uses only the lower
> 32-bits of the value. It is quite likely that the TSC adjustment results
> in them increasing more rapidly then they should.
>   

Or that the TSC is terribly miscalibrated.  Here is the log of all 48 
guests.  In this case, the host detects 1995.008 as the frequency.  This 
is a Barcelona.  I suspect that we're masking the 
X86_FEATURE_CONSTANT_TSC though.

 From a quick look, I suspect that the number of wildly off TSC 
calibrations correspond to the VMs that are misbehaving.  I think this 
may mean that we have to re-examine the tsc delta computation.

10_serial.log:time.c: Detected 1995.038 MHz processor.
11_serial.log:time.c: Detected 2363.195 MHz processor.
12_serial.log:time.c: Detected 2492.675 MHz processor.
13_serial.log:time.c: Detected 1995.061 MHz processor.
14_serial.log:time.c: Detected 1994.917 MHz processor.
15_serial.log:time.c: Detected 4100.735 MHz processor.
16_serial.log:time.c: Detected 2075.800 MHz processor.
17_serial.log:time.c: Detected 2674.350 MHz processor.
18_serial.log:time.c: Detected 1995.002 MHz processor.
19_serial.log:time.c: Detected 1994.978 MHz processor.
1_serial.log:time.c: Detected 4384.310 MHz processor.
20_serial.log:time.c: Detected 1994.969 MHz processor.
21_serial.log:time.c: Detected 3670.696 MHz processor.
22_serial.log:time.c: Detected 1994.997 MHz processor.
23_serial.log:time.c: Detected 2218.613 MHz processor.
24_serial.log:time.c: Detected 1995.048 MHz processor.
25_serial.log:time.c: Detected 1995.015 MHz processor.
26_serial.log:time.c: Detected 1994.957 MHz processor.
27_serial.log:time.c: Detected 1995.051 MHz processor.
28_serial.log:time.c: Detected 1995.021 MHz processor.
29_serial.log:time.c: Detected 3679.640 MHz processor.
2_serial.log:time.c: Detected 2191.105 MHz processor.
30_serial.log:time.c: Detected 1995.086 MHz processor.
31_serial.log:time.c: Detected 1995.071 MHz processor.
32_serial.log:time.c: Detected 1995.051 MHz processor.
33_serial.log:time.c: Detected 2331.760 MHz processor.
34_serial.log:time.c: Detected 1995.011 MHz processor.
35_serial.log:time.c: Detected 1995.050 MHz processor.
36_serial.log:time.c: Detected 1994.911 MHz processor.
37_serial.log:time.c: Detected 1994.905 MHz processor.
38_serial.log:time.c: Detected 1994.881 MHz processor.
39_serial.log:time.c: Detected 1995.027 MHz processor.
3_serial.log:time.c: Detected 2051.467 MHz processor.
40_serial.log:time.c: Detected 1994.987 MHz processor.
41_serial.log:time.c: Detected 1994.970 MHz processor.
42_serial.log:time.c: Detected 1994.952 MHz processor.
43_serial.log:time.c: Detected 1995.042 MHz processor.
44_serial.log:time.c: Detected 1994.998 MHz processor.
45_serial.log:time.c: Detected 1995.016 MHz processor.
46_serial.log:time.c: Detected 1995.006 MHz processor.
47_serial.log:time.c: Detected 1995.000 MHz processor.
4_serial.log:time.c: Detected 1995.112 MHz processor.
5_serial.log:time.c: Detected 1995.081 MHz processor.
6_serial.log:time.c: Detected 2017.303 MHz processor.
7_serial.log:time.c: Detected 1995.046 MHz processor.
8_serial.log:time.c: Detected 1994.951 MHz processor.
9_serial.log:time.c: Detected 2184.754 MHz processor.

Regards,

Anthony Liguori

> So can you try setting KVM_MAX_PIT_INTR_INTERVAL to a lower value? HZ/10
> or something.
>
> You can confirm this theory by booting the guests with "apic=debug".
>
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