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: Tue, 30 May 2017 11:27:05 +0200	[thread overview]
Message-ID: <20170530092705.GC26792@aepfle.de> (raw)
In-Reply-To: <20170524153315.GO18530@char.us.oracle.com>

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On Wed, May 24, Konrad Rzeszutek Wilk wrote:

> Is there some form of tests that they can run to verify and test
> that this is safe? Or perhaps this is something that is based on the kernel
> versions? Like 4.11 are safe, but 3.18 is not?

I'm not sure why you are asking for specific kernel versions.

But the test is simply to boot a HVM domU with 'tsc_mode=native' and
migrate it to a similar dom0. This fails with 3.12 and 4.4 based domU
kernels, with xen-4.7 as dom0. This pretty much ruins the plan.

So far I have not investigated why the domU on the remote side does not
get any cpu time, or why it makes no progress. But in the end the I
think only a hardware upgrade to TSC-scaling capable CPUs will avoid the
performance penalty due to the TSC emulation.
I do not have access to such hardware to verify it.

Olaf

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