Re: [PATCH] xen: preserve native TSC speed during migration between identical hosts

From: Olaf Hering <olaf@aepfle.de>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
	xen-devel@lists.xen.org, Ian Jackson <ian.jackson@eu.citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH] xen: preserve native TSC speed during migration between identical hosts
Date: Wed, 24 May 2017 17:25:03 +0200	[thread overview]
Message-ID: <20170524152503.GB6930@aepfle.de> (raw)
In-Reply-To: <20170524150940.GI18530@char.us.oracle.com>

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On Wed, May 24, Konrad Rzeszutek Wilk wrote:

> How can that be determined? As in how can the guest (domU) be within
> the range? Is there some way to determine that? Is there some
> matrix of the various OS-es that can tolerate this?

Just cycle through all dom0s and look for the cpu_khz values:
 # xl dmesg | grep -w MHz
(XEN) Detected 2494.018 MHz processor.

What I have seen are ranges up to 200khz, even if /proc/cpuinfo says
"2.50GHz" . Some dom0s calibrated themselves to exactly 2500.000 MHz,
they do not need a tolerance.

The expected frequency of a given domU can be seen in 'dump softtsc
stats' (s). How various guest kernels deal with the slightly different
frequency, no idea.

Olaf

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