From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olaf Hering <olaf@aepfle.de>
Subject: Re: [PATCH v12] tolerate jitter in cpu_khz calculation
 to avoid TSC emulation
Date: Mon, 11 Mar 2019 11:26:53 +0100
Message-ID: <20190311112653.0f9997b4.olaf@aepfle.de>
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To: Jan Beulich <JBeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wei.liu2@citrix.com>, xen-devel <xen-devel@lists.xenproject.org>, Roger Pau Monne <roger.pau@citrix.com>
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Am Mon, 11 Mar 2019 04:02:14 -0600
schrieb "Jan Beulich" <JBeulich@suse.com>:

> > One interesting aspect is: the xenlinux based kernels report clocksourc=
e=3Dtsc, =20
> I don't think they do - iirc they are hardcoded to clocksource=3Dxen.

For HVM they do:

 # dmesg | grep -Ei '(clock|hz)'
[    0.000000] hpet clockevent registered
[    0.000000] tsc: Detected 2000.225 MHz processor
[    0.142074] smpboot: CPU0: Intel(R) Xeon(R) CPU           E5504  @ 2.00G=
Hz (fam: 06, model: 1a, stepping: 05)
[    0.322108] hpet0: 3 comparators, 64-bit 62.500000 MHz counter
[    0.324095] Switched to clocksource hpet
[    2.436321] tsc: Refined TSC clocksource calibration: 2000.084 MHz
[    3.437123] Switched to clocksource tsc

But PV shows just that:

 # dmesg | grep -Ei '(clock|hz)'
[    0.000000] Xen reported: 2000.084 MHz processor.
[    0.316671] Switched to clocksource xen

> > There was even that 'independent_wallclock' knob. Why is that? =20
> Why is what? Are you questioning the presence of the setting in
> the XenoLinux kernels, or its absence in the pv-ops ones?

I'm just curious why HVM uses tsc, but nothing states that using ntpd would=
 be a requirement.

However, a brief search suggests that reported "clock issues" are indeed so=
lved by running ntp in HVM.

Olaf

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