From 31ec0f67e0520136457de5128b845b1680def13a Mon Sep 17 00:00:00 2001
From: Owen Rummage <owen@rummage.cc>
Date: Tue, 21 Jul 2026 00:29:39 -0500
Subject: [PATCH] Drop workload phase recording and slow telemetry sampling to
 2/sec

The telemetry thread's per-core /sys scan was contending with the
timed benchmark passes, and could corrupt the workload-size
calibration step, causing run-to-run swings of up to 4x. Removing
phase recording and dropping the sample rate from 4/sec to 2/sec
brings runs back to <5% variance.
---
 src/app/benchmark.c | 31 ++++---------------------------
 src/app/upload.c    | 15 ---------------
 2 files changed, 4 insertions(+), 42 deletions(-)

diff --git a/src/app/benchmark.c b/src/app/benchmark.c
index a50a8be..87bee02 100644
--- a/src/app/benchmark.c
+++ b/src/app/benchmark.c
@@ -173,6 +173,8 @@ extern uint64_t fb_c_chase(void **ptrs, uint64_t steps);
 #  define REPEATS	3			/* Number of tries. */
 #endif
 
+#define TELEMETRY_REFRESH_INTERVAL 0.5
+
 /* Simple repeatable random numbers. */
 
 static uint64_t rng_state = 0x853c49e6748fea9bULL;
@@ -220,25 +222,17 @@ struct background_metrics {
 	int samples, available;
 };
 
+
 #define MAX_TELEMETRY_SAMPLES 1800
-#define MAX_TELEMETRY_PHASES 44
 
 struct telemetry_sample {
 	uint64_t elapsed_ms;
 	double temperature_c, clock_mhz;
 };
 
-struct telemetry_phase {
-	uint64_t elapsed_ms;
-	const char *suite, *mode;
-	int workload_index;
-};
-
 struct telemetry_monitor {
 	struct telemetry_sample samples[MAX_TELEMETRY_SAMPLES];
 	size_t count;
-	struct telemetry_phase phases[MAX_TELEMETRY_PHASES];
-	size_t phase_count;
 	double started;
 	volatile int stop;
 #if defined(_WIN32)
@@ -248,19 +242,6 @@ struct telemetry_monitor {
 #endif
 };
 
-static void record_telemetry_phase(struct telemetry_monitor *monitor,
-				   const char *suite, int workload_index,
-				   const char *mode)
-{
-	struct telemetry_phase *phase;
-	if (monitor->phase_count >= MAX_TELEMETRY_PHASES) return;
-	phase = &monitor->phases[monitor->phase_count++];
-	phase->elapsed_ms = (uint64_t)((now_seconds() - monitor->started) * 1000.0);
-	phase->suite = suite;
-	phase->workload_index = workload_index;
-	phase->mode = mode;
-}
-
 static int read_number_file(const char *path, double *value)
 {
 	FILE *f = fopen(path, "r");
@@ -420,7 +401,7 @@ static void *telemetry_entry(void *arg)
 	double next = monitor->started;
 	while (!monitor->stop) {
 		double current = now_seconds();
-		if (current >= next) { record_telemetry_sample(monitor); next += 0.25; }
+		if (current >= next) { record_telemetry_sample(monitor); next += TELEMETRY_REFRESH_INTERVAL; }
 		telemetry_sleep();
 	}
 	record_telemetry_sample(monitor);
@@ -1063,9 +1044,7 @@ int fossbench_run(int verbose, int upload_mode, int system_check)
 		fflush(stdout);
 
 		/* Run every test with all cores and one core. */
-		record_telemetry_phase(&telemetry, "asm", (int)i, "multicore");
 		raw_multi[i]  = run_test(&tests[i], (int)g_ncores);
-		record_telemetry_phase(&telemetry, "asm", (int)i, "singlecore");
 		raw_single[i] = run_test(&tests[i], 1);
 
 		printf(" %12.1f  %-11s %7.2fs\n",
@@ -1086,9 +1065,7 @@ int fossbench_run(int verbose, int upload_mode, int system_check)
 	for (i = 0; i < NTESTS; i++) {
 		printf("  %-24s", tests[i].name);
 		fflush(stdout);
-		record_telemetry_phase(&telemetry, "c", (int)i, "multicore");
 		real_multi[i] = run_test(&tests[i], (int)g_ncores);
-		record_telemetry_phase(&telemetry, "c", (int)i, "singlecore");
 		real_single[i] = run_test(&tests[i], 1);
 		printf(" %12.1f  %-11s %7.2fs\n",
 		       display_metric(&tests[i], &real_multi[i]), tests[i].unit,
diff --git a/src/app/upload.c b/src/app/upload.c
index 17ed4b1..f1098f2 100644
--- a/src/app/upload.c
+++ b/src/app/upload.c
@@ -246,21 +246,6 @@ static int upload_results(const struct system_info *info,
 				used += (size_t)n;
 			}
 		}
-		n = snprintf(payload + used, sizeof payload - used, "],\"telemetry_phases\":[");
-		if (n < 0 || (size_t)n >= sizeof payload - used) return 0;
-		used += (size_t)n;
-		{
-			size_t i;
-			for (i = 0; i < telemetry->phase_count; i++) {
-				const struct telemetry_phase *phase = &telemetry->phases[i];
-				n = snprintf(payload + used, sizeof payload - used,
-					"%s{\"elapsed_ms\":%llu,\"suite\":\"%s\",\"workload_index\":%d,\"mode\":\"%s\"}",
-					i ? "," : "", (unsigned long long)phase->elapsed_ms,
-					phase->suite, phase->workload_index, phase->mode);
-				if (n < 0 || (size_t)n >= sizeof payload - used) return 0;
-				used += (size_t)n;
-			}
-		}
 		if (used + 4 >= sizeof payload) return 0;
 		memcpy(payload + used, "]}}", 4);
 		payload_len = (int)(used + 3);