[Qemu-devel] [PATCH] test-coroutine: add baseline test that times the cost of function calls

[Paolo Bonzini <pbonzini@redhat.com>]

This can be used to compute the cost of coroutine operations.  In the
end the cost of the function call is a few clock cycles, so it's pretty
cheap for now, but it may become more relevant as the coroutine code
is optimized.

For example, here are the results on my machine:

   Function call 100000000 iterations: 0.173884 s
   Yield 100000000 iterations: 8.445064 s
   Lifecycle 1000000 iterations: 0.098445 s
   Nesting 10000 iterations of 1000 depth each: 7.406431 s

One yield takes 83 nanoseconds, one enter takes 97 nanoseconds,
one coroutine allocation takes (roughly, since some of the allocations
in the nesting test do hit the pool) 739 nanoseconds:

   (8.445064 - 0.173884) * 10^9 / 100000000 = 82.7
   (0.098445 * 100 - 0.173884) * 10^9 / 100000000 = 96.7
   (7.406431 * 10 - 0.173884) * 10^9 / 100000000 = 738.9

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 tests/test-coroutine.c | 24 ++++++++++++++++
 1 files changed, 24 insertions(+)

diff --git a/tests/test-coroutine.c b/tests/test-coroutine.c
index 760636d..6e634f4 100644
--- a/tests/test-coroutine.c
+++ b/tests/test-coroutine.c
@@ -288,6 +288,29 @@ static void perf_yield(void)
         maxcycles, duration);
 }
 
+static __attribute__((noinline)) void dummy(unsigned *i)
+{
+    (*i)--;
+}
+
+static void perf_baseline(void)
+{
+    unsigned int i, maxcycles;
+    double duration;
+
+    maxcycles = 100000000;
+    i = maxcycles;
+
+    g_test_timer_start();
+    while (i > 0) {
+        dummy(&i);
+    }
+    duration = g_test_timer_elapsed();
+
+    g_test_message("Function call %u iterations: %f s\n",
+        maxcycles, duration);
+}
+
 int main(int argc, char **argv)
 {
     g_test_init(&argc, &argv, NULL);
@@ -301,6 +324,7 @@ int main(int argc, char **argv)
         g_test_add_func("/perf/lifecycle", perf_lifecycle);
         g_test_add_func("/perf/nesting", perf_nesting);
         g_test_add_func("/perf/yield", perf_yield);
+        g_test_add_func("/perf/function-call", perf_baseline);
     }
     return g_test_run();
 }
-- 
1.9.3