kallsyms: optimize things a bit #1785
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ti-mo
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May 21, 2025
Add a few fast benchmarks to make optimization easier. Signed-off-by: Timo Beckers <[email protected]>
It's possible for /proc/kallsyms to contain utf8, by virtue of the kernel
treating symbol names as bags of bytes. Needless to say these symbols are
going to be rare in the wild, if they exist at all.
Do not pessimise the common case of parsing an all-ASCII kallsyms table
by checking for invalid utf8. This means that invalid utf8 will not be
rejected anymore, while valid encodings continue to work as before.
```
goos: linux
goarch: amd64
pkg: github.com/cilium/ebpf/internal/kallsyms
cpu: AMD Ryzen 7 3700X 8-Core Processor
│ old.txt │ new.txt │
│ sec/op │ sec/op vs base │
AssignModules-16 4.740µ ± 3% 3.326µ ± 0% -29.85% (p=0.002 n=6)
AssignAddresses-16 6.327µ ± 1% 4.187µ ± 1% -33.82% (p=0.002 n=6)
AssignModulesKallsyms-16 376.3m ± 1% 307.1m ± 3% -18.40% (p=0.002 n=6)
AssignAddressesKallsyms-16 405.5m ± 5% 322.7m ± 2% -20.41% (p=0.002 n=6)
geomean 1.463m 1.084m -25.90%
│ old.txt │ new.txt │
│ B/op │ B/op vs base │
AssignModules-16 4.242Ki ± 0% 4.258Ki ± 0% +0.37% (p=0.002 n=6)
AssignAddresses-16 4.438Ki ± 0% 4.453Ki ± 0% +0.35% (p=0.002 n=6)
AssignModulesKallsyms-16 8.260Mi ± 0% 8.260Mi ± 0% ~ (p=0.777 n=6)
AssignAddressesKallsyms-16 12.29Mi ± 0% 12.29Mi ± 0% ~ (p=0.167 n=6)
geomean 211.6Ki 212.0Ki +0.18%
│ old.txt │ new.txt │
│ allocs/op │ allocs/op vs base │
AssignModules-16 9.000 ± 0% 11.000 ± 0% +22.22% (p=0.002 n=6)
AssignAddresses-16 19.00 ± 0% 21.00 ± 0% +10.53% (p=0.002 n=6)
AssignModulesKallsyms-16 323.6k ± 0% 323.6k ± 0% ~ (p=1.000 n=6) ¹
AssignAddressesKallsyms-16 536.6k ± 0% 536.6k ± 0% ~ (p=1.000 n=6)
geomean 2.334k 2.517k +7.81%
¹ all samples are equal
```
Signed-off-by: Lorenz Bauer <[email protected]>
Co-authored-by: Timo Beckers <[email protected]>
We currently allocate a lot of small strings to hold symbol and
module name. This happens even if we aren't interested in that
specific symbol.
Use the map[string([]byte)] optimization to remove temporary
allocations.
```
goos: linux
goarch: amd64
pkg: github.com/cilium/ebpf/internal/kallsyms
cpu: AMD Ryzen 7 3700X 8-Core Processor
│ old.txt │ new.txt │
│ sec/op │ sec/op vs base │
AssignModules-16 3.326µ ± 0% 3.009µ ± 2% -9.53% (p=0.002 n=6)
AssignAddresses-16 4.187µ ± 1% 3.351µ ± 1% -19.98% (p=0.002 n=6)
AssignModulesKallsyms-16 307.1m ± 3% 294.3m ± 7% -4.15% (p=0.002 n=6)
AssignAddressesKallsyms-16 322.7m ± 2% 301.7m ± 2% -6.52% (p=0.002 n=6)
geomean 1.084m 972.6µ -10.26%
│ old.txt │ new.txt │
│ B/op │ B/op vs base │
AssignModules-16 4.258Ki ± 0% 4.172Ki ± 0% -2.02% (p=0.002 n=6)
AssignAddresses-16 4.453Ki ± 0% 4.141Ki ± 0% -7.02% (p=0.002 n=6)
AssignModulesKallsyms-16 8458.543Ki ± 0% 4.312Ki ± 0% -99.95% (p=0.002 n=6)
AssignAddressesKallsyms-16 12586.352Ki ± 0% 4.219Ki ± 0% -99.97% (p=0.002 n=6)
geomean 212.0Ki 4.210Ki -98.01%
│ old.txt │ new.txt │
│ allocs/op │ allocs/op vs base │
AssignModules-16 11.000 ± 0% 5.000 ± 0% -54.55% (p=0.002 n=6)
AssignAddresses-16 21.000 ± 0% 3.000 ± 0% -85.71% (p=0.002 n=6)
AssignModulesKallsyms-16 323560.00 ± 0% 12.00 ± 0% -100.00% (p=0.002 n=6)
AssignAddressesKallsyms-16 536565.000 ± 0% 7.000 ± 0% -100.00% (p=0.002 n=6)
geomean 2.517k 5.958 -99.76%
```
Signed-off-by: Lorenz Bauer <[email protected]>
Co-authored-by: Timo Beckers <[email protected]>
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Two small optimisations which drop CPU time by 25% on my machine, plus a lot less allocations.