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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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