From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andre Przywara <andre.przywara@amd.com>
Subject: Re: 2.6.35-rc1 regression with pvclock and smp guests
Date: Tue, 27 Jul 2010 14:21:02 +0200
Message-ID: <4C4ECF2E.4070103@amd.com>
References: <4C483F67.1010007@amd.com> <4C4BF96B.7010005@redhat.com> <4C4D4B8B.80006@amd.com> <4C4EAEFC.20207@redhat.com> <4C4EC7D1.6030708@amd.com> <4C4ECBC7.1070405@redhat.com>
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Cc: "glommer@redhat.com" <glommer@redhat.com>,
	Zachary Amsden <zamsden@redhat.com>,
	KVM list <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
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Avi Kivity wrote:
>   On 07/27/2010 02:49 PM, Andre Przywara wrote:
>>> What is the guest executing when it hangs?
>> Both VCPUs are halted, the monitor and System.map tell me it's in=20
>> native_safe_halt().
>> The code sequence confirms this, it is an intentional sti;hlt condit=
ion.
>> Using -smp 16 also shows that all 16 VCPUs are stuck.
>>
>=20
> Well, strange.  The intent of that patch was to make the clock never =
go=20
> backwards.  Perhaps the change made it go forwards by a large amount,=
=20
> and the guest is not hung, just waiting for some timer that is far in=
=20
> the future.
>=20
> Can you do something like
>=20
> -      if (ret < last)
> +      if (ret < last) {
> +            static u64 max_delta;
> +            if (last - ret > max_delta) {
> +                  max_delta =3D last - ret;
> +                  printk("advancing kvmclock by: %llx\n", max_delta)=
;
> +            }
>               return last;
> +      }
>=20
> to see if this is happening?
No change, it still hangs. I also don't see the printk.
The output with smp=3D1 is like this:
[    1.186549] ACPI: Power Button [PWRF]
[    1.189204] XENFS: not registering filesystem on non-xen platform
[    1.195001] Non-volatile memory driver v1.3
[    1.196358] Linux agpgart interface v0.103
[    1.197687] [drm] Initialized drm 1.1.0 20060810
[    1.198926] [drm:i915_init] *ERROR* drm/i915 can't work without=20
intel_agp module!
[    1.201213] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
=FF[    1.460714] serial8250: ttyS0 at I/O 0x3f8 (irq =3D 4) is a 16550=
A
[    1.463243] 00:06: ttyS0 at I/O 0x3f8 (irq =3D 4) is a 16550A
[    1.467153] brd: module loaded
[    1.469245] loop: module loaded
With smp=3D2 the output stops just before the strange "y" character (I=20
guess it's ASCII 255), which I assume is an artifact of the serial cons=
ole.
As you can see at the timestamps, it takes some time between the last=20
shown line (1.201213) and the first missing one (1.460714).

Thanks,
Andre.

--=20
Andre Przywara
AMD-OSRC (Dresden)
Tel: x29712