Re: [RFC] vPMU support for AMD system

[Wei Huang <wei@redhat.com>]

This

On 10/4/14 2:00 AM, Gleb Natapov wrote:
> Hi,
>
> On Tue, Sep 30, 2014 at 09:07:22PM -0500, Wei Huang wrote:
>> Hi Paolo and Gleb,
>>
>> The attached file is a preliminary version of AMD vPMU support for KVM.
>> Currently I am working on a formal patch set; but realized that there are
>> some design choice to make (see below). I thought it is better to send it
>> out now, asking for your comments before sending out patchset v1.
>>
>> If you are OK with current approach, please let me know. Otherwise please
>> share your suggestions/comments on the design choice (see suggestions
>> below). I will send out split patch set soon.
>>
> I am not very familiar with AMD PMU, but IIRC is lacks architectural PMU, so the
> first question that comes to my mind is:
>
>> +static struct kvm_event_hw_type_mapping amd_event_mapping[] = {
>> +	[0] = { 0x76, 0x00, PERF_COUNT_HW_CPU_CYCLES },
>> +	[1] = { 0xc0, 0x00, PERF_COUNT_HW_INSTRUCTIONS },
>> +	[3] = { 0x80, 0x00, PERF_COUNT_HW_CACHE_REFERENCES },
>> +	[4] = { 0x81, 0x00, PERF_COUNT_HW_CACHE_MISSES },
>> +	[5] = { 0xc4, 0x00, PERF_COUNT_HW_BRANCH_INSTRUCTIONS },
>> +	[6] = { 0xc5, 0x00, PERF_COUNT_HW_BRANCH_MISSES },
>> +};
>> +
> Are those evens count exactly same things on all AMD cpus?
These mappings were pulled off from Linux perf code. From the code and 
several AMD BKDGs I read, they were consistent across CPU families.

If there is no guaranteed consistency, I think we can fall back to raw 
perf counters. So this amd_event_mapping table can be removed.

-Wei

>
>
> --
> 			Gleb.
>