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0dfbe4c646
Ian reports an issue that the metric DRAM_BW_Use often remains 0. The metric expression for DRAM_BW_Use on CLX/SKX: "( 64 * ( uncore_imc@cas_count_read@ + uncore_imc@cas_count_write@ ) / 1000000000 ) / duration_time" The counts of uncore_imc/cas_count_read/ and uncore_imc/cas_count_write/ are scaled up by 64, that is to turn a count of cache lines into bytes, the count is then divided by 1000000000 to give GB. However, the counts of uncore_imc/cas_count_read/ and uncore_imc/cas_count_write/ have been scaled yet. The scale values are from sysfs, such as /sys/devices/uncore_imc_0/events/cas_count_read.scale. It's 6.103515625e-5 (64 / 1024.0 / 1024.0). So if we use original metric expression, the result is not correct. But the difficulty is, for SKL client, the counts are not scaled. The metric expression for DRAM_BW_Use on SKL: "64 * ( arb@event\\=0x81\\,umask\\=0x1@ + arb@event\\=0x84\\,umask\\=0x1@ ) / 1000000 / duration_time / 1000" root@kbl-ppc:~# perf stat -M DRAM_BW_Use -a -- sleep 1 Performance counter stats for 'system wide': 190 arb/event=0x84,umask=0x1/ # 1.86 DRAM_BW_Use 29,093,178 arb/event=0x81,umask=0x1/ 1,000,703,287 ns duration_time 1.000703287 seconds time elapsed The result is expected. So the easy way is just change the metric expression for CLX/SKX. This patch changes the metric expression to: "( ( ( uncore_imc@cas_count_read@ + uncore_imc@cas_count_write@ ) * 1048576 ) / 1000000000 ) / duration_time" 1048576 = 1024 * 1024. Before (tested on CLX): root@lkp-csl-2sp5 ~# perf stat -M DRAM_BW_Use -a -- sleep 1 Performance counter stats for 'system wide': 765.35 MiB uncore_imc/cas_count_read/ # 0.00 DRAM_BW_Use 5.42 MiB uncore_imc/cas_count_write/ 1001515088 ns duration_time 1.001515088 seconds time elapsed After: root@lkp-csl-2sp5 ~# perf stat -M DRAM_BW_Use -a -- sleep 1 Performance counter stats for 'system wide': 767.95 MiB uncore_imc/cas_count_read/ # 0.80 DRAM_BW_Use 5.02 MiB uncore_imc/cas_count_write/ 1001900010 ns duration_time 1.001900010 seconds time elapsed Fixes: |
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