the topdown metric is not accurate

[shaileneF]

Hello, there is a situation that the topdown metric is not accurate.
I found that you are reading top-down events in the following way

            cFrontendBoundSlots = extract_bits(perfMetrics, 16, 23);
            cBadSpeculationSlots = extract_bits(perfMetrics, 8, 15);
            cBackendBoundSlots = extract_bits(perfMetrics, 24, 31);
            cRetiringSlots = extract_bits(perfMetrics, 0, 7);
            const double total = double(cFrontendBoundSlots + cBadSpeculationSlots + cBackendBoundSlots + cRetiringSlots);
            if (total != 0)
            {
                cFrontendBoundSlots = m->FrontendBoundSlots[core_id] += uint64((double(cFrontendBoundSlots) / total) * double(slots));
                cBadSpeculationSlots = m->BadSpeculationSlots[core_id] += uint64((double(cBadSpeculationSlots) / total) * double(slots));
                cBackendBoundSlots = m->BackendBoundSlots[core_id] += uint64((double(cBackendBoundSlots) / total) * double(slots));
                cRetiringSlots = m->RetiringSlots[core_id] += uint64((double(cRetiringSlots) / total) * double(slots));
            }

So you didn't handle the overflow of top-down events？
I found that the metric backend_bound is very high and the metric frontend_bound is very low. Does is related to the overflow? why didn't you handle the overflow, maybe it doesn't need to handle this? 
Could you tell me some way to collect topdown metrics by configure and read the register?
Thank you and I am looking forward to your response!

[rdementi]

here you can find more detail about this method: https://dyninst.github.io/scalable_tools_workshop/petascale2018/assets/slides/TMA%20addressing%20challenges%20in%20Icelake%20-%20Ahmad%20Yasin.pdf

check out the slide 16 (PERF_METRIC register). The counter can't overflow because it always reports a ratio in HW.