lzxpress/test: time performance of long boring sequences

We get *very* slow when long runs of the bytes are the same. On this
laptop the test takes 18s; with the next commit it will be 0.006s.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

diff --git a/lib/compression/testsuite.c b/lib/compression/testsuite.c
index 4de3700c727e779e8316f4b314f3d8140b71af24..708af2bcbf1493ee64fbd829f6e60f187d959199 100644 (file)
--- a/lib/compression/testsuite.c
+++ b/lib/compression/testsuite.c
@@ -340,6 +340,73 @@ static bool test_lzxpress4(struct torture_context *test)
        return true;
 }
 
+
+static bool test_lzxpress_many_zeros(struct torture_context *test)
+{
+       /*
+        * Repeated values (zero is convenient but not special) will lead to
+        * very long substring searches in compression, which can be very slow
+        * if we're not careful.
+        *
+        * This test makes a very loose assertion about how long it should
+        * take to compress a million zeros.
+        *
+        * Wall clock time *should* be < 0.1 seconds with the fix and around a
+        * minute without it. We try for CLOCK_THREAD_CPUTIME_ID which should
+        * filter out some noise on the machine, and set the threshold at 5
+        * seconds.
+        */
+
+       TALLOC_CTX *tmp_ctx = talloc_new(test);
+       const size_t N_ZEROS = 1000000;
+       const uint8_t *zeros = talloc_zero_size(tmp_ctx, N_ZEROS);
+       const ssize_t expected_c_size = 93;
+       ssize_t c_size;
+       uint8_t *comp, *decomp;
+       static struct timespec t_start, t_end;
+       uint64_t elapsed_ns;
+
+       if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &t_start) != 0) {
+               if (clock_gettime(CUSTOM_CLOCK_MONOTONIC, &t_start) != 0) {
+                       clock_gettime(CLOCK_REALTIME, &t_start);
+               }
+       }
+
+       comp = talloc_zero_size(tmp_ctx, 2048);
+
+       c_size = lzxpress_compress(zeros,
+                                  N_ZEROS,
+                                  comp,
+                                  talloc_get_size(comp));
+
+       torture_assert_int_equal(test, c_size, expected_c_size,
+                                "fixed lzxpress_compress size");
+
+       decomp = talloc_size(tmp_ctx, N_ZEROS * 2);
+       c_size = lzxpress_decompress(comp,
+                                    c_size,
+                                    decomp,
+                                    N_ZEROS * 2);
+
+       if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &t_end) != 0) {
+               if (clock_gettime(CUSTOM_CLOCK_MONOTONIC, &t_end) != 0) {
+                       clock_gettime(CLOCK_REALTIME, &t_end);
+               }
+       }
+       elapsed_ns = (
+               (t_end.tv_sec - t_start.tv_sec) * 1000U * 1000U * 1000U) +
+               (t_end.tv_nsec - t_start.tv_nsec);
+       torture_comment(test, "round-trip time: %lu ns\n", elapsed_ns);
+       torture_assert(test, elapsed_ns < 3 * 1000U * 1000U * 1000U,
+                      "million zeros round trip tool > 3 seconds");
+       torture_assert_mem_equal(test, decomp, zeros, N_ZEROS,
+                                "fixed lzxpress_decompress data");
+
+       talloc_free(tmp_ctx);
+       return true;
+}
+
+
 static bool test_lzxpress_round_trip(struct torture_context *test)
 {
        /*
@@ -408,6 +475,8 @@ struct torture_suite *torture_local_compression(TALLOC_CTX *mem_ctx)
        torture_suite_add_simple_test(suite, "lzxpress2", test_lzxpress2);
        torture_suite_add_simple_test(suite, "lzxpress3", test_lzxpress3);
        torture_suite_add_simple_test(suite, "lzxpress4", test_lzxpress4);
+       torture_suite_add_simple_test(suite, "lzxpress_many_zeros",
+                                     test_lzxpress_many_zeros);
        torture_suite_add_simple_test(suite, "lzxpress_round_trip",
                                      test_lzxpress_round_trip);
        return suite;

diff --git a/selftest/knownfail.d/lzxpress b/selftest/knownfail.d/lzxpress
new file mode 100644 (file)
index 0000000..0c3a6d3
--- /dev/null
+++ b/selftest/knownfail.d/lzxpress
@@ -0,0 +1 @@
+samba4.local.compression.lzxpress_many_zeros
\ No newline at end of file