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, 14 insertions, 12 deletions

diff --git a/tests/benchmark-crypto-cipher.c b/tests/benchmark-crypto-cipher.c
index 3ca31a2779..53032334ec 100644
--- a/tests/benchmark-crypto-cipher.c
+++ b/tests/benchmark-crypto-cipher.c
@@ -21,11 +21,12 @@ static void test_cipher_speed(size_t chunk_size,
 {
     QCryptoCipher *cipher;
     Error *err = NULL;
-    double total = 0.0;
     uint8_t *key = NULL, *iv = NULL;
     uint8_t *plaintext = NULL, *ciphertext = NULL;
     size_t nkey;
     size_t niv;
+    const size_t total = 2 * GiB;
+    size_t remain;
 
     if (!qcrypto_cipher_supports(alg, mode)) {
         return;
@@ -58,33 +59,34 @@ static void test_cipher_speed(size_t chunk_size,
                                       &err) == 0);
 
     g_test_timer_start();
-    do {
+    remain = total;
+    while (remain) {
         g_assert(qcrypto_cipher_encrypt(cipher,
                                         plaintext,
                                         ciphertext,
                                         chunk_size,
                                         &err) == 0);
-        total += chunk_size;
-    } while (g_test_timer_elapsed() < 1.0);
+        remain -= chunk_size;
+    }
+    g_test_timer_elapsed();
 
-    total /= MiB;
     g_print("Enc chunk %zu bytes ", chunk_size);
-    g_print("%.2f MB/sec ", total / g_test_timer_last());
+    g_print("%.2f MB/sec ", (double)total / MiB / g_test_timer_last());
 
-    total = 0.0;
     g_test_timer_start();
-    do {
+    remain = total;
+    while (remain) {
         g_assert(qcrypto_cipher_decrypt(cipher,
                                         plaintext,
                                         ciphertext,
                                         chunk_size,
                                         &err) == 0);
-        total += chunk_size;
-    } while (g_test_timer_elapsed() < 1.0);
+        remain -= chunk_size;
+    }
+    g_test_timer_elapsed();
 
-    total /= MiB;
     g_print("Dec chunk %zu bytes ", chunk_size);
-    g_print("%.2f MB/sec ", total / g_test_timer_last());
+    g_print("%.2f MB/sec ", (double)total / MiB / g_test_timer_last());
 
     qcrypto_cipher_free(cipher);
     g_free(plaintext);