From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@suse.com>
Subject: Re: [PATCH 06/13] x86/hvm: Scale host TSC when
 setting/getting guest TSC
Date: Tue, 27 Oct 2015 02:15:53 -0600
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To: Haozhong Zhang <haozhong.zhang@intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Jun Nakajima <jun.nakajima@intel.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, xen-devel@lists.xen.org, Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>, Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>, Keir Fraser <keir@xen.org>, Boris Ostrovsky <boris.ostrovsky@oracle.com>
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>>> On 27.10.15 at 02:54, <haozhong.zhang@intel.com> wrote:
> On Thu, Oct 22, 2015 at 08:17:29AM -0600, Jan Beulich wrote:
>> >>> On 28.09.15 at 09:13, <haozhong.zhang@intel.com> wrote:
>> > The existing hvm_set_guest_tsc_fixed() and hvm_get_guest_tsc_fixed()
>> > calculate the guest TSC by adding the TSC offset to the host TSC. When
>> > the TSC scaling is enabled, the host TSC should be scaled first. This
>> > patch adds the scaling logic to those two functions.
>> 
>> Just like mentioned for the first twp patches - I'd first of all like to
>> understand why the lack of scaling this wasn't an issue for SVM so
>> far. What you reads plausible, but assuming that SVM TSC scaling
>> code was tested, I'm hesitant to apply changes to it without
>> understanding the details (or at least without SVM maintainers'
>> consent).
>>
> 
> The current SVM TSC ratio code does not seem correct w/o patch 6 (as
> well as patch 2, but I only analyze patch 6 here). Following is the
> explanation.

Right - as said before, all you write reads plausible, but will need
confirming by an SVM maintainer. And then I'd like to ask you to
re-order you patch series to fix bugs first (whether that's along
with generalizing or ahead of it I'd leave to you, as long as the
result meets the main goal I'm having here: backportability).

Jan