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Demonstrations of llcstat.
llcstat traces cache reference and cache miss events system-wide, and summarizes
them by PID and CPU.
These events, defined in uapi/linux/perf_event.h, have different meanings on
different architecture. For x86-64, they mean misses and references to LLC.
Example output:
# ./llcstat.py 20 -c 5000
Running for 20 seconds or hit Ctrl-C to end.
PID NAME CPU REFERENCE MISS HIT%
0 swapper/15 15 3515000 640000 81.79%
238 migration/38 38 5000 0 100.00%
4512 ntpd 11 5000 0 100.00%
150867 ipmitool 3 25000 5000 80.00%
150895 lscpu 17 280000 25000 91.07%
151807 ipmitool 15 15000 5000 66.67%
150757 awk 2 15000 5000 66.67%
151213 chef-client 5 1770000 240000 86.44%
151822 scribe-dispatch 12 15000 0 100.00%
123386 mysqld 5 5000 0 100.00%
[...]
Total References: 518920000 Total Misses: 90265000 Hit Rate: 82.61%
This shows each PID's cache hit rate during the 20 seconds run period.
A count of 5000 was used in this example, which means that one in every 5,000
events will trigger an in-kernel counter to be incremented. This is refactored
on the output, which is why it is always in multiples of 5,000.
We don't instrument every single event since the overhead would be prohibitive,
nor do we need to: this is a type of sampling profiler. Because of this, the
processes that trigger the 5,000'th cache reference or misses can happen to
some degree by chance. Overall it should make sense. But for low counts,
you might find a case where -- by chance -- a process has been tallied with
more misses than references, which would seem impossible.
# ./llcstat.py 10 -t
Running for 10 seconds or hit Ctrl-C to end.
PID TID NAME CPU REFERENCE MISS HIT%
170843 170845 docker 12 2700 1200 55.56%
298670 298670 kworker/15:0 15 500 0 100.00%
170254 170254 kworker/11:1 11 2500 400 84.00%
1046952 1046953 git 0 2600 1100 57.69%
170843 170849 docker 15 1000 400 60.00%
1027373 1027382 node 8 3500 2500 28.57%
0 0 swapper/7 7 173000 4200 97.57%
1028217 1028217 node 14 15600 22400 0.00%
[...]
Total References: 7139900 Total Misses: 1413900 Hit Rate: 80.20%
This shows each TID`s cache hit rate during the 10 seconds run period.
USAGE message:
# ./llcstat.py --help
usage: llcstat.py [-h] [-c SAMPLE_PERIOD] [duration]
Summarize cache references and misses by PID
positional arguments:
duration Duration, in seconds, to run
optional arguments:
-h, --help show this help message and exit
-c SAMPLE_PERIOD, --sample_period SAMPLE_PERIOD
Sample one in this many number of cache reference
and miss events
-t, --tid Summarize cache references and misses by PID/TID