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Context:
- We usually write software in user space (outside the OS's kernel, e.g: user apps like utilities, programming languages, GUI...).
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Problem:
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When profiling the application: if we do it from user space (e.g: pprof) => result is not reliable because there will be some overhead of each layer on top of the CPU/ memory.
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2 initial options:
- Edit the Kernel Source Code: not really practical since the usecase is trivial amount. (pending for years to be adopted by distros)
- Write a Kernel Model: this is more practical however, regular maintenance is inevitable as keeping up with the new kernel versions + risking corrupting the Kernel (e.g: if the module has a bug => crash the whole system)
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Solution:
- BPF was originally used in Linux to filter network packets.
- eBPF (Extended Berkeley Packet Filter) allows to trace syscalls, user space/ library functions, network packets... => system performance, monitoring, security...
- How it works:
- Pre-defined hooks: system calls, function entry/exit, kernel tracepoints, network events...
- eBPF programs are event-driven, run at certain hook point then:
- Safe checked by Verifier
- Then compiled by JIT compiler from bytecode to instructions
- Execute the desired code right before actual system calls
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Conclusion:
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Context:
- PGO (Profile-Guided Optimization) is introduced in Go version 1.20, a.k.a FDO (feedback-directed optimization), a technique collects and feeds the profile data back to the next compilier build.
- From the 2nd build/release, expectedly improving 2-14% performance (on-going for future builds)
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Problem:
- Grab wanted to experiment this to some of their services: use self-managed database TalariaDB, orchestrated service and a monorepo one.
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Results:
- In a service cluster's image that uses TalariaDB, add -PGO=./talaria.PGO to the go build command: 10% CPU usage reduction, 30% memory usage reduction and 38% volume usage reduction.
- On the orchestrated service: the reduction is only around 5% << the effort the enable PGO => not substaintial
- Monorepo service is currently not supported since needing a seperated pprof service and a build process supporting PGO arguments to attach/retrieve pprof file
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Conclusion:
- Applicable on simple, yet low-effort deployed services
