Re: [Xen-devel] [PATCH 2/2] [RFC] xen/console: Provide timestamps as an offset since boot.

[Tim Deegan <tim@xxxxxxx>]

At 14:03 +0000 on 27 Feb (1393506187), Andrew Cooper wrote:
> Some latent bugs are emphasised by these changes.  There are steps in time
> when the TSC scale is calculated, and when the platform time is initialised 
> ...
> 
>     (XEN) [    0.000000] Using scheduler: SMP Credit Scheduler (credit)
>     (XEN) [   27.553075] Detected 2793.232 MHz processor.
>     (XEN) [   27.558277] Initing memory sharing.
>     (XEN) [   27.562502] Cannot set CPU feature mask on CPU#0
>     (XEN) [   27.567852] mce_intel.c:717: MCA Capability: BCAST 0 SER 0 CMCI 
> 0 firstbank 0 extended MCE MSR 18
>     (XEN) [   27.577687] Intel machine check reporting enabled
>     (XEN) [   27.583147] PCI: MCFG configuration 0: base e0000000 segment 
> 0000 buses 00 - 3f
>     (XEN) [   27.591407] PCI: MCFG area at e0000000 reserved in E820
>     (XEN) [   27.597369] PCI: Using MCFG for segment 0000 bus 00-3f
>     (XEN) [   27.603238] I/O virtualisation disabled
>     (XEN) [   27.608093] ENABLING IO-APIC IRQs
>     (XEN) [   27.612136]  -> Using new ACK method
>     (XEN) [   27.616601] ..TIMER: vector=0xF0 apic1=0 pin1=2 apic2=-1 pin2=-1
>     (XEN) [    0.153431] Platform timer is 14.318MHz HPET

The patch below fixes the first step for me.  I haven't been able to
understand the exact mechanism of the second one yet.  With this patch
applied, of course, the second step is not visible -- which doesn't
mean it's gone away.

Cheers,

Tim.

commit d986516ce297bbcf3181225105dbc67edfa7c37e
Author: Tim Deegan <tim@xxxxxxx>
Date:   Thu Feb 27 16:17:02 2014 +0000

    x86/time: Always count s_time from Xen boot.
    
    In the early-boot clock, before the calibration routines kick in,
    count time from Xen boot rather than from when the BSP's TSC was 0.
    
    Signed-off-by: Tim Deegan <tim@xxxxxxx>

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 82492c1..2bc2b2d 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -1456,6 +1456,7 @@ void __init early_time_init(void)
     u64 tmp = init_pit_and_calibrate_tsc();
 
     set_time_scale(&this_cpu(cpu_time).tsc_scale, tmp);
+    rdtscll(this_cpu(cpu_time).local_tsc_stamp);
 
     do_div(tmp, 1000);
     cpu_khz = (unsigned long)tmp;


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