branchstats

Overview ¶

Command branchstats analyzes branch profiles for branch mispredict rates.

branchstats expects a perf.data collected with

perf record -e branches -j any -c 400009

To collect only branches in user-space code, use

perf record -e branches:u -j any,u -c 400009

The output is a table like

comm     PC                               branches mispredicts
bench    scanner.go:258                  419609441 309206957 (73.7%)
    257 func isLetter(ch rune) bool {
    258         return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' || ch >= 0x80 && unicode.IsLetter(ch)
    259 }

bench    mgcmark.go:1000                1967244262 236405319 (12.0%)
    999 }
   1000 if bits&bitPointer == 0 {
   1001         continue // not a pointer

Each row shows a branch at a particular location and gives the estimated number of times that branch executed, the estimated number of mispredicts, and the mispredict rate. The table is sorted by the number of mispredicts.