bench: add perf stat/record wrappers

bench/lib/perf.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# perf wrappers for bench/.
+
+PERF_EVENTS="task-clock,cycles,instructions,cache-references,cache-misses,page-faults,context-switches"
+
+perf_paranoid_ok() {
+    local v
+    v=$(cat /proc/sys/kernel/perf_event_paranoid 2>/dev/null || echo 99)
+    [ "$v" -le 2 ]
+}
+
+perf_stat_run() {
+    local out_csv="$1" cmd="$2"
+    perf stat -x, -o "$out_csv" -e "$PERF_EVENTS" -- sh -c "$cmd" >/dev/null 2>&1
+}
+
+perf_record_run() {
+    local out_data="$1" cmd="$2"
+    perf record -F 99 -g --quiet -o "$out_data" -- sh -c "$cmd" >/dev/null 2>&1
+}
+
+# perf_stat_metric <csv> <event> → numeric value or "null"
+# perf stat -x, format: <value>,<unit>,<event>,<runtime>,<pct>,...
+perf_stat_metric() {
+    local csv="$1" event="$2"
+    awk -F',' -v ev="$event" '
+        # skip comment/header lines starting with #
+        /^#/ { next }
+        $3 == ev { print $1; found=1; exit }
+        END { if (!found) print "null" }
+    ' "$csv"
+}