runners: bench: Added a small bench probe cache

The idea here is to try to use the string pointer itself to bypass
strcmps and the O(n) scan.

It doesn't seem to have any impact on our current bench runtime, but it
doesn't hurt to keep around.

runners/bench_runner.c

@@ -945,6 +945,11 @@ typedef struct bench_record {
     bench_ns_t start_simtime;
 } bench_record_t;
 
+typedef struct bench_cache {
+    const char *probe;
+    size_t i;
+} bench_cache_t;
+
 bench_probe_t *bench_probes = NULL;
 size_t bench_probe_count = 0;
 size_t bench_probe_capacity = 0;
@@ -957,9 +962,13 @@ bench_record_t *bench_records = NULL;
 size_t bench_record_count = 0;
 size_t bench_record_capacity = 0;
 
+#define BENCH_CACHE_COUNT 64
+bench_cache_t bench_cache[BENCH_CACHE_COUNT];
+
 void bench_init(const struct lfs3_cfg *cfg) {
     bench_cfg = cfg;
     bench_record_count = 0;
+    memset(bench_cache, 0, sizeof(bench_cache));
 }
 
 // needed in bench_deinit
@@ -978,6 +987,12 @@ void bench_deinit(const struct lfs3_cfg *cfg) {
 }
 
 bench_record_t *bench_find(const char *probe) {
+    // cached?
+    bench_cache_t *cache = &bench_cache[(size_t)probe % BENCH_CACHE_COUNT];
+    if (cache->probe == probe) {
+        return &bench_records[cache->i];
+    }
+
     // find our record
     bench_record_t *record = NULL;
     for (size_t i = 0; i < bench_record_count; i++) {
@@ -1041,6 +1056,9 @@ bench_record_t *bench_find(const char *probe) {
         }
     }
 
+    // add to cache
+    cache->probe = probe;
+    cache->i = record - bench_records;
     return record;
 }