add end-to-end IO benchmarks and fix pprof-identified hotspots - #128
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Add comprehensive benchmark suite (io_bench_test.go): - BenchmarkEndToEndRead/Write: full SCSI stack (512B to 256KB) - BenchmarkEndToEndReadParallel/WriteParallel: concurrent IO - BenchmarkFileBackingStoreRead/Write: isolated backing store pprof-guided optimizations: - Guard hot-path log.Debugf with log.GetLevel() check in scsi.go, sbc.go, backingstore.go — eliminates 22% CPU overhead from logrus Entry allocation even when debug logging is disabled - Add FileBackingStore.ReadAt for zero-copy reads directly into caller's buffer, bypassing Read()'s per-call make([]byte, tl) - Use ReadAt via interface assertion in bsPerformCommand to read directly into InSDBBuffer, eliminating allocation + copy Results (256KB reads): +42% throughput, allocs reduced from 10 to 5 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Designed benchmark programs for read/write IO paths, used pprof CPU+memory profiling to identify hotspots, and fixed them.
Benchmark Suite (
io_bench_test.go)BenchmarkEndToEndRead/Write— full SCSI stack: AddCommandQueue -> SBCReadWrite -> FileBackingStore (512B/4KB/64KB/256KB)BenchmarkEndToEndReadParallel/WriteParallel— concurrent 4KB IOBenchmarkFileBackingStoreRead/Write— isolated backing store layerpprof Findings & Fixes
1. logrus debug logging: 22% CPU (FIXED)
log.Debugf()in hot paths (scsi.go:101, sbc.go:436, backingstore.go:161) was allocating logrus Entry objects even when debug level was disabled. Fixed by guarding withlog.GetLevel() >= log.DebugLevel.2. FileBackingStore.Read allocation: 38% memory (FIXED)
Every read allocated
make([]byte, tl)then copied to InSDBBuffer. AddedReadAt(buf, offset)method to FileBackingStore, used via interface assertion in bsPerformCommand to read directly into InSDBBuffer — zero allocation, zero copy.Results (256KB reads)
Test plan
go build ./...passesgo vet ./...passesgo test ./...all tests pass