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

From: "Jan Beulich" <JBeulich@suse.com>
To: Olaf Hering <olaf@aepfle.de>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Wei Liu <wei.liu2@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xen.org
Subject: Re: [PATCH] xen: preserve native TSC speed during migration between identical hosts
Date: Tue, 30 May 2017 01:27:49 -0600	[thread overview]
Message-ID: <592D3B15020000780015D793@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20170530064108.GB26792@aepfle.de>

>>> On 30.05.17 at 08:41, <olaf@aepfle.de> wrote:
> On Mon, May 29, Jan Beulich wrote:
> 
>> Finally I don't think a host wide option will do. If it is to be of use
>> (considering that it used wrong may break applications), it needs
>> to be per-domain, and its value needs to be migrated (perhaps
>> in the form of a low/high pair of TSC frequency values).
> 
> How is it supposed to be propagated from one host to another?
> 
> With the global option one can unconditionally receive a domU and
> preserve "native performance" in case of tsc_mode=default. With a
> per-domU option one has to know upfront.

I don't understand: If the incoming stream tells you the acceptable
clock range, what else do you need to know (upfront or later)?

Jan

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