Thanks. I get the point about sampling, but my question was more about the sources of memory accesses. In previous answer, you told me that the PERF_SAMPLE_IP field is filled with "the IP of a random core on the socket that happens to read the uncore registers", so my last question is about the result presented by perf mem report tool.
This tool (like perf report) reports a Symbol and a Shared Object colums. I am thus wondering how can the entries in these columns be correct if the IP for each sample is wrong ? Manu 2014/1/7 Andi Kleen <a...@firstfloor.org>: > Manuel Selva <selva.man...@gmail.com> writes: > > >> The perf mem record tool use the >> MEM_INST_RETIRED.LATENCY_ABOVE_THRESHOLD which I guess belongs to the >> memory PEBS events you mentionned (isn't it ?) is reporting > > Yes. > >> information about the sources of the events. it seems that for this >> purpose the IP information is used, does it mean that what perf mem >> reports can be wrong because of the random IP selection mechanism you >> mentionned ? > > The CPU can theoretically execute billions of loads/stores every second. > There is no way any reporting mechanism can keep up with that. > So the only thing you can do is to sample (only collect > every N operations), with a fairly large period. > > -Andi > > -- > a...@linux.intel.com -- Speaking for myself only -- To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
