tests: benchmark crypto with fixed data size, not time period

Currently the crypto benchmarks are processing data in varying chunk
sizes, over a fixed time period. This turns out to be a terrible idea
because with small chunk sizes the overhead of checking the elapsed
time on each loop iteration masks the true performance.

Benchmarking over a fixed data size avoids the loop running any system
calls which can interfere with the performance measurements.

Before this change

Enc chunk 512 bytes 2283.47 MB/sec Dec chunk 512 bytes 2236.23 MB/sec OK
Enc chunk 4096 bytes 2744.97 MB/sec Dec chunk 4096 bytes 2614.71 MB/sec OK
Enc chunk 16384 bytes 2777.53 MB/sec Dec chunk 16384 bytes 2678.44 MB/sec OK
Enc chunk 65536 bytes 2809.34 MB/sec Dec chunk 65536 bytes 2699.47 MB/sec OK

After this change

Enc chunk 512 bytes 2058.22 MB/sec Dec chunk 512 bytes 2030.11 MB/sec OK
Enc chunk 4096 bytes 2699.27 MB/sec Dec chunk 4096 bytes 2573.78 MB/sec OK
Enc chunk 16384 bytes 2748.52 MB/sec Dec chunk 16384 bytes 2653.76 MB/sec OK
Enc chunk 65536 bytes 2814.08 MB/sec Dec chunk 65536 bytes 2712.74 MB/sec OK

The actual crypto performance hasn't changed, which shows how
significant the mis-measurement has been for small data sizes.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

1 files changed, 9 insertions, 8 deletions

diff --git a/tests/benchmark-crypto-hash.c b/tests/benchmark-crypto-hash.c
index 9b6f7a9155..7f659f7323 100644
--- a/tests/benchmark-crypto-hash.c
+++ b/tests/benchmark-crypto-hash.c
@@ -20,7 +20,8 @@ static void test_hash_speed(const void *opaque)
     size_t chunk_size = (size_t)opaque;
     uint8_t *in = NULL, *out = NULL;
     size_t out_len = 0;
-    double total = 0.0;
+    const size_t total = 2 * GiB;
+    size_t remain;
     struct iovec iov;
     int ret;
 
@@ -31,20 +32,20 @@ static void test_hash_speed(const void *opaque)
     iov.iov_len = chunk_size;
 
     g_test_timer_start();
-    do {
+    remain = total;
+    while (remain) {
         ret = qcrypto_hash_bytesv(QCRYPTO_HASH_ALG_SHA256,
                                   &iov, 1, &out, &out_len,
                                   NULL);
         g_assert(ret == 0);
 
-        total += chunk_size;
-    } while (g_test_timer_elapsed() < 5.0);
+        remain -= chunk_size;
+    }
+    g_test_timer_elapsed();
 
-    total /= MiB;
     g_print("sha256: ");
-    g_print("Testing chunk_size %zu bytes ", chunk_size);
-    g_print("done: %.2f MB in %.2f secs: ", total, g_test_timer_last());
-    g_print("%.2f MB/sec\n", total / g_test_timer_last());
+    g_print("Hash %zu GB chunk size %zu bytes ", total / GiB, chunk_size);
+    g_print("%.2f MB/sec ", (double)total / MiB / g_test_timer_last());
 
     g_free(out);
     g_free(in);