Re: Understanding perf mem -t load results

[Manuel Selva <selva.manuel@gmail.com>]

On 12/24/2013 08:28 AM, Andi Kleen wrote:
> On Tue, Dec 24, 2013 at 08:10:10AM +0100, Manuel Selva wrote:
>> "You cannot use uncore events to sample IPs" means that the values
>> corresponding to PERF_SAMPLE_IP are not correct ? Some benchmarks I
>> did by sampling ME_INST_RETIRED with PERF_SAMPLE_IP let me think
>> that I was able to get the source of th event. The IP value was
>> coherent. Maybe this is not always the case.
>
> It's the IP of a random core on the socket that happens to read the uncore
> registers.
>

Ok. Where should I have read this information, in the Intel Software 
Developer’s Manual volume 3B (I guess this is a hardware limitation) ?

I checked what can be measured with the offcore facility. I can ask to 
count remote memory accesses, but now I am not sure PEBS is enable for 
these events. If the answer is no, I can't accurately identify remote 
memory accesses with offcore events ? As a consequence I am wondering if 
there is a way to do such thing ?

Manu