Re: [PATCH 00/13] Add VMX TSC scaling support

From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	Haozhong Zhang <haozhong.zhang@intel.com>,
	xen-devel@lists.xen.org
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>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>,
	Jan Beulich <jbeulich@suse.com>, Keir Fraser <keir@xen.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Subject: Re: [PATCH 00/13] Add VMX TSC scaling support
Date: Mon, 28 Sep 2015 09:48:49 -0400	[thread overview]
Message-ID: <56094541.4060904@oracle.com> (raw)
In-Reply-To: <56091BA5.8090604@citrix.com>

On 09/28/2015 06:51 AM, Andrew Cooper wrote:
> On 28/09/15 08:13, Haozhong Zhang wrote:
>> This patchset adds support for VMX TSC scaling feature which is
>> available on Intel Skylake CPU. The specification of VMX TSC scaling
>> can be found at
>> http://www.intel.com/content/www/us/en/processors/timestamp-counter-scaling-virtualization-white-paper.html
>>
>> VMX TSC scaling allows guest TSC which is read by guest rdtsc(p)
>> instructions increases in a rate that is customized by the hypervisor
>> and can be different than the host TSC rate. Basically, VMX TSC
>> scaling adds a 64-bit field called TSC multiplier in VMCS so that, if
>> VMX TSC scaling is enabled, TSC read by guest rdtsc(p) instructions
>> will be calculated by the following formula:
>>
>>    guest EDX:EAX = (Host TSC * TSC multiplier) >> 48 + VMX TSC Offset
>>
>> where, Host TSC = Host MSR_IA32_TSC + Host MSR_IA32_TSC_ADJUST.
>>
>> This patchset is composed of following four parts.
>>    1. PATCH 01 - 02 fix bugs in tsc_get_info() which could result in
>>       errors when VMX TSC scaling is used.
>>       
>>    2. PATCH 03 - 09 add/move the common parts of VMX TSC scaling and
>>       SVM TSC ratio to hvm.c and x86/time.c.
>>       
>>    3. PATCH 10 - 12 implement the VMX-specific code for supporting VMX
>>       TSC scaling.
>>       
>>    4. PATCH 13 adapts libxl for VMX TSC scaling (as well as SVM TSC
>>       ratio).
> Thankyou for this series.  I have had a brief look over it and it
> appears to be in good shape, but have not done a thorough review yet.
>
> Konrad/Boris: As Oracle are the main users of the more interesting guest
> timing modes, do you have tests to verify correct functioning?

Not really. The most interesting thing to test here I think would be 
migration between differently-clocked systems and we only do save/restore.

-boris