[PATCH 1/2] selftests/resctrl: fastcat for benchmarking counter reads

[Peter Newman <peternewman@google.com>]

This patch is provided for reference and not intended for submission.

This test program is used to evaluate the cost of reading resctrl
counters. It is essentially a drop-in replacement for cat, allowing
presumably small files, like resctrl nodes, to be read repeatedly using
pread(). In contrast, repeated invocations of cat would open and close
the counter files, which is an order of magnitude more costly than the
actual counter file read operations.

For example, the steps below were used to determine the cost of reading
a large number of local or remote counters on a dual-socket AMD Zen2:

Bind to a CPU in L3 domain 6:

 # taskset -c 25 bash

Record the setup cost for the groups /sys/fs/resctrl/mon_groups/*:

 # cd /sys/fs/resctrl
 # FASTCAT_READ_COUNT=0 perf stat -r 1000 /tmp/fastcat mon_groups/*/mon_data/mon_L3_06/mbm_*

Measure local read cost:

 # perf stat -r 1000 /tmp/fastcat mon_groups/*/mon_data/mon_L3_06/mbm_*

Measure remote read cost:

 # perf stat -r 1000 /tmp/fastcat mon_groups/*/mon_data/mon_L3_07/mbm_*

Signed-off-by: Peter Newman <peternewman@google.com>
---
 tools/testing/selftests/resctrl/.gitignore |  1 +
 tools/testing/selftests/resctrl/Makefile   |  6 ++-
 tools/testing/selftests/resctrl/fastcat.c  | 63 ++++++++++++++++++++++
 3 files changed, 68 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/resctrl/fastcat.c

diff --git a/tools/testing/selftests/resctrl/.gitignore b/tools/testing/selftests/resctrl/.gitignore
index ab68442b6bc8d..11a40e331f4ad 100644
--- a/tools/testing/selftests/resctrl/.gitignore
+++ b/tools/testing/selftests/resctrl/.gitignore
@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0-only
 resctrl_tests
+fastcat
diff --git a/tools/testing/selftests/resctrl/Makefile b/tools/testing/selftests/resctrl/Makefile
index f408bd6bfc3d4..c5ec1e8289390 100644
--- a/tools/testing/selftests/resctrl/Makefile
+++ b/tools/testing/selftests/resctrl/Makefile
@@ -3,10 +3,12 @@
 CFLAGS = -g -Wall -O2 -D_FORTIFY_SOURCE=2
 CFLAGS += $(KHDR_INCLUDES)
 
-TEST_GEN_PROGS := resctrl_tests
+TEST_GEN_PROGS := resctrl_tests fastcat
 
 LOCAL_HDRS += $(wildcard *.h)
 
 include ../lib.mk
 
-$(OUTPUT)/resctrl_tests: $(wildcard *.c)
+$(OUTPUT)/resctrl_tests: cache.c cat_test.c cmt_test.c fill_buf.c mba_test.c mbm_test.c resctrlfs.c resctrl_tests.c resctrl_val.c
+
+$(OUTPUT)/fastcat: fastcat.c
diff --git a/tools/testing/selftests/resctrl/fastcat.c b/tools/testing/selftests/resctrl/fastcat.c
new file mode 100644
index 0000000000000..ac7a56f82a7c2
--- /dev/null
+++ b/tools/testing/selftests/resctrl/fastcat.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int main(int argc, char **argv)
+{
+	int nfiles = argc - 1;
+	char *nread_str;
+	int nread;
+	int *fds;
+	int i, j;
+
+	nread_str = getenv("FASTCAT_READ_COUNT");
+	if (!nread_str)
+		nread = 1;
+	else
+		nread = atoi(nread_str);
+
+	if (nfiles < 1)
+		exit(1);
+
+	fds = malloc(sizeof(*fds) * (argc));
+	if (!fds) {
+		perror("malloc");
+		exit(1);
+	}
+
+	printf("opening %d files\n", nfiles);
+
+	for (i = 1; i < argc; i++) {
+		fds[i - 1] = open(argv[i], O_RDONLY);
+		if (fds[i - 1] < 0) {
+			perror(argv[i]);
+			exit(1);
+		}
+	}
+
+	printf("reading %d files %d times\n", nfiles, nread);
+
+	for (j = 0; j < nread; j++) {
+		for (i = 0; i < nfiles; i++) {
+			// Assumed to be large enough for any output of
+			// mbm_*_bytes
+			char buf[40];
+			ssize_t r;
+
+			r = pread(fds[i], buf, sizeof(buf), 0);
+			if (r < 0) {
+				perror(argv[i + 1]);
+				exit(1);
+			}
+		}
+	}
+
+	printf("closing %d files\n", nfiles);
+	for (i = 0; i < nfiles; i++)
+		close(fds[i]);
+
+	return 0;
+}

base-commit: 81983758430957d9a5cb3333fe324fd70cf63e7e
-- 
2.47.0.199.ga7371fff76-goog