Re: Understanding perf mem -t load results

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

On 12/24/2013 10:27 PM, Andi Kleen wrote:
>> 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 ?
>
> The OFFCORE events are not PEBS enabled.

Ok, you confirm what I read in the Intel SDM.

However the memory PEBS
> events report the same information (with some limitations) in
> the PEBS record (and perf reports this information)
By memory PEBS events, do you mean the following events ?

MEM_LOAD_RETIRED.L1D_MISS
MEM_LOAD_RETIRED.L1D_LINE_MISS
MEM_LOAD_RETIRED.L2_MISS
MEM_LOAD_RETIRED.L2_LINE_MISS
MEM_LOAD_RETIRED.DTLB_MISS

I can't profile memory accesses with these events, isn't it ? What do 
you mean by perf reports this infomation, which perf tool ?

>
> In general you cannot accurately profile all memory accesses.

Does it means that the perf mem record tool is reporting wrong values 
concerning the source of the event ? (I checked that this tool use the 
load latency event with PEBS and you said that the IP reported by this 
uncore event is not always the correct one ?)

Thanks,

----
Manu