diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c
index 854f0108d8e6..e4f1cea317f1 100644
--- a/tools/testing/selftests/resctrl/fill_buf.c
+++ b/tools/testing/selftests/resctrl/fill_buf.c
@@ -88,18 +88,6 @@ static int fill_one_span_read(unsigned char *buf, size_t buf_size)
 	return sum;
 }
 
-static void fill_one_span_write(unsigned char *buf, size_t buf_size)
-{
-	unsigned char *end_ptr = buf + buf_size;
-	unsigned char *p;
-
-	p = buf;
-	while (p < end_ptr) {
-		*p = '1';
-		p += (CL_SIZE / 2);
-	}
-}
-
 void fill_cache_read(unsigned char *buf, size_t buf_size, bool once)
 {
 	int ret = 0;
@@ -114,15 +102,6 @@ void fill_cache_read(unsigned char *buf, size_t buf_size, bool once)
 	*value_sink = ret;
 }
 
-static void fill_cache_write(unsigned char *buf, size_t buf_size, bool once)
-{
-	while (1) {
-		fill_one_span_write(buf, buf_size);
-		if (once)
-			break;
-	}
-}
-
 unsigned char *alloc_buffer(size_t buf_size, int memflush)
 {
 	void *buf = NULL;
@@ -151,7 +130,7 @@ unsigned char *alloc_buffer(size_t buf_size, int memflush)
 	return buf;
 }
 
-int run_fill_buf(size_t buf_size, int memflush, int op)
+int run_fill_buf(size_t buf_size, int memflush)
 {
 	unsigned char *buf;
 
@@ -159,10 +138,7 @@ int run_fill_buf(size_t buf_size, int memflush, int op)
 	if (!buf)
 		return -1;
 
-	if (op == 0)
-		fill_cache_read(buf, buf_size, false);
-	else
-		fill_cache_write(buf, buf_size, false);
+	fill_cache_read(buf, buf_size, false);
 
 	free(buf);
 
diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
index 51f5f4b25e06..ba1ce1b35699 100644
--- a/tools/testing/selftests/resctrl/resctrl.h
+++ b/tools/testing/selftests/resctrl/resctrl.h
@@ -142,7 +142,7 @@ int perf_event_open(struct perf_event_attr *hw_event, pid_t pid, int cpu,
 unsigned char *alloc_buffer(size_t buf_size, int memflush);
 void mem_flush(unsigned char *buf, size_t buf_size);
 void fill_cache_read(unsigned char *buf, size_t buf_size, bool once);
-int run_fill_buf(size_t buf_size, int memflush, int op);
+int run_fill_buf(size_t buf_size, int memflush);
 int initialize_mem_bw_imc(void);
 int measure_mem_bw(const struct user_params *uparams,
 		   struct resctrl_val_param *param, pid_t bm_pid,
diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
index bee4123a5a9b..60627dbae20a 100644
--- a/tools/testing/selftests/resctrl/resctrl_tests.c
+++ b/tools/testing/selftests/resctrl/resctrl_tests.c
@@ -265,13 +265,16 @@ int main(int argc, char **argv)
 			ksft_exit_fail_msg("Out of memory!\n");
 		uparams.benchmark_cmd[1] = span_str;
 		uparams.benchmark_cmd[2] = "1";
-		uparams.benchmark_cmd[3] = "0";
 		/*
+		 * Third parameter was previously used for "operation"
+		 * (read/write) of which only (now default) "read"/"0"
+		 * works.
 		 * Fourth parameter was previously used to indicate
 		 * how long "fill_buf" should run for, with "false"
 		 * ("fill_buf" will keep running until terminated)
 		 * the only option that works.
 		 */
+		uparams.benchmark_cmd[3] = NULL;
 		uparams.benchmark_cmd[4] = NULL;
 		uparams.benchmark_cmd[5] = NULL;
 	}
diff --git a/tools/testing/selftests/resctrl/resctrl_val.c b/tools/testing/selftests/resctrl/resctrl_val.c
index 5331354aaf64..8b5973c5e934 100644
--- a/tools/testing/selftests/resctrl/resctrl_val.c
+++ b/tools/testing/selftests/resctrl/resctrl_val.c
@@ -622,8 +622,8 @@ int measure_mem_bw(const struct user_params *uparams,
  */
 static void run_benchmark(int signum, siginfo_t *info, void *ucontext)
 {
-	int operation, ret, memflush;
 	char **benchmark_cmd;
+	int ret, memflush;
 	size_t span;
 	FILE *fp;
 
@@ -643,9 +643,8 @@ static void run_benchmark(int signum, siginfo_t *info, void *ucontext)
 		/* Execute default fill_buf benchmark */
 		span = strtoul(benchmark_cmd[1], NULL, 10);
 		memflush =  atoi(benchmark_cmd[2]);
-		operation = atoi(benchmark_cmd[3]);
 
-		if (run_fill_buf(span, memflush, operation))
+		if (run_fill_buf(span, memflush))
 			fprintf(stderr, "Error in running fill buffer\n");
 	} else {
 		/* Execute specified benchmark */
