From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olaf Hering <olaf@aepfle.de>
Subject: Re: [PATCH v5] new config option vtsc_tolerance_khz to
 avoid TSC emulation
Date: Thu, 29 Mar 2018 10:58:34 +0200
Message-ID: <20180329085834.GI30726@aepfle.de>
References: <20180327092655.28530-1-olaf@aepfle.de>
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To: Roger Pau =?utf-8?B?TW9ubsOp?= <roger.pau@citrix.com>
Cc: Tim Deegan <tim@xen.org>, Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wei.liu2@citrix.com>, George Dunlap <George.Dunlap@eu.citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Marek =?utf-8?Q?Marczykowski-G=C3=B3recki?= <marmarek@invisiblethingslab.com>, xen-devel@lists.xen.org, Julien Grall <julien.grall@arm.com>, Jan Beulich <jbeulich@suse.com>
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On Thu, Mar 29, Roger Pau Monn=C3=A9 wrote:

> AFAICT in the chunk above you will disable vtsc without checking if
> the hardware supports TSC scaling, which leads to inaccurate TSC values
> on hardware that could provide accurate results without the software
> emulation overhead.

Is that really the case? Maybe I get the logic wrong, but what I see is:
what ever my change does, or if a HVM domain runs on a host with scaling
feature, disable vtsc. hvm_get_tsc_scaling_ratio has no side effects.
Isnt the purpose to not emulate vtsc if the hardware supports scaling?

Olaf

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