When experimenting with perf I wanted to have separate counts for events in
userspace and the kernel. I used:
$ perf stat -e instructions:u -e instructions:k -e cycles:u -e cycles:k -e
cache-misses:u -e cache-misses:k make
The associated output below includes the event modifiers for all the events,
but the 3.06 and 0.37 insns per cycles look off. Shouldn't that
instructions:u/cycles:u and instructions:k/cycles:k be the values reported for
"insns per cycle"?
Performance counter stats for 'make':
340,034,597,510 instructions:u # 3.06 insns per cycle
[83.70%]
40,963,149,231 instructions:k # 0.37 insns per cycle
[83.67%]
185,451,244,302 cycles:u [83.54%]
36,901,938,457 cycles:k [83.64%]
34,811,408 cache-misses:u
[83.96%]
102,781,614 cache-misses:k
[83.85%]
66.290033775 seconds time elapsed
For the L1-icache-load-misses and iTLB-load-misses the event modifier appears
to be dropped as shown in the output below
$ perf stat -e instructions:u -e instructions:k -e cycles:u -e cycles:k -e
L1-icache-load-misses:u -e L1-icache-load-misses:k make
Performance counter stats for 'make':
340,522,617,398 instructions:u # 3.09 insns per cycle
[83.55%]
41,045,130,555 instructions:k # 0.37 insns per cycle
[83.82%]
184,082,319,783 cycles:u [84.12%]
36,447,301,873 cycles:k [84.21%]
849,438,930 L1-icache-load-misses
[82.96%]
445,141,089 L1-icache-load-misses
[83.67%]
65.611650172 seconds time elapsed
$ perf stat -e instructions:u -e instructions:k -e cycles:u -e cycles:k -e
iTLB-load-misses:u -e iTLB-load-misses:k make
2,074,873,836,988 instructions:u # 2.09 insns per cycle
[83.47%]
128,412,604,104 instructions:k # 0.13 insns per cycle
[83.51%]
1,786,252,236,017 cycles:u [83.52%]
202,469,325,995 cycles:k [83.46%]
786,419,505 iTLB-load-misses
[83.44%]
40,548,044 iTLB-load-misses
[83.43%]
3800.440742009 seconds time elapsed
It appears that the output is listing the measurements in the same order they
are specified on the command line, but it would be nice if the output was
clearer on the events being measured. If I am reading the output correctly,
the L1-icache-load-misses per instruction is pretty poor for kernel-space.
Much of the time I am looking at ratios of events and it would be nice if "perf
stat" had a way to have it compute the ratios directly. Maybe a "-m, --math"
option allowing algebraic expressions where you could do:
perf stat -e instructions:u -e instructions:k -e cycles:u -e cycles:k -e
L1-icache-load-misses:u -e L1-icache-load-misses:k \
--math instructions:u/icache-load-misses:u \
--math instructions:k/icache-load-misses:k \
make
Performance counter stats for 'make':
$ perf stat -e instructions:u -e instructions:k -e cycles:u -e cycles:k -e
L1-icache-load-misses:u -e L1-icache-load-misses:k make
Performance counter stats for 'make':
340,522,617,398 instructions:u # 3.09 insns per cycle
[83.55%]
41,045,130,555 instructions:k # 0.37 insns per cycle
[83.82%]
184,082,319,783 cycles:u [84.12%]
36,447,301,873 cycles:k [84.21%]
849,438,930 L1-icache-load-misses
[82.96%]
445,141,089 L1-icache-load-misses
[83.67%]
401.09 instructions:u/icache-load-misses:u
92.20 instructions:k/icache-load-misses:k
65.611650172 seconds time elapsed
-Will
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