[igt-dev] [PATCH i-g-t] tests/dumb_buffer: Try to compute the largest possible dumb buffer

[Chris Wilson]

For our threaded clear test, we want to create as many buffers as can
fit into the available memory. However, since we don't know the size of
that available memory, it can be easy to create too large or too many
buffers, and waste our time testing the unobtainable. Instead, try
probing the available space by trying to create the largest dumb buffer
we possibly can, and assume that is the equivalent to the available
space.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Ramalingam C <ramalingam.c at intel.com>
---
 tests/dumb_buffer.c | 68 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 59 insertions(+), 9 deletions(-)

diff --git a/tests/dumb_buffer.c b/tests/dumb_buffer.c
index 3d2dc9966..c1e7b4d3b 100644
--- a/tests/dumb_buffer.c
+++ b/tests/dumb_buffer.c
@@ -31,18 +31,18 @@
  * combinations are rejected.
  */
 
-#include <stdlib.h>
-#include <sys/ioctl.h>
-#include <stdio.h>
-#include <string.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
-#include <errno.h>
-#include <sys/stat.h>
-#include <sys/time.h>
-#include <getopt.h>
 #include <pthread.h>
+#include <signal.h>
 #include <stdatomic.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/time.h>
 
 #include <drm.h>
 
@@ -325,12 +325,62 @@ static void *thread_clear(void *data)
 	return (void *)(uintptr_t)checked;
 }
 
+static jmp_buf sigjmp;
+
+static void sigprobe(int sig)
+{
+	longjmp(sigjmp, sig);
+}
+
+static uint64_t estimate_largest_dumb_buffer(int fd)
+{
+	sighandler_t old_sigbus = signal(SIGBUS, sigprobe);
+	sighandler_t old_sigsegv = signal(SIGSEGV, sigprobe);
+	struct drm_mode_create_dumb create = {
+		.bpp = 32,
+		.width = 1 << 20, /* in pixels */
+		.height = 1, /* in rows */
+	};
+	volatile uint64_t largest = 0;
+	char * volatile ptr = NULL;
+
+	if (setjmp(sigjmp)) {
+		if (ptr)
+			munmap(ptr, create.size);
+
+		signal(SIGBUS, old_sigbus);
+		signal(SIGSEGV, old_sigsegv);
+
+		igt_info("Largest dumb buffer sucessfully created: %'"PRIu64" bytes\n",
+			 largest);
+		return largest / PAGE_SIZE;
+	}
+
+	for (create.height = 1; create.height; create.height *= 2) {
+		if (__dumb_create(fd, &create))
+			longjmp(sigjmp, SIGABRT);
+
+		ptr = __dumb_map(fd, create.handle, create.size, PROT_READ);
+		dumb_destroy(fd, create.handle);
+		if (!ptr)
+			longjmp(sigjmp, SIGABRT);
+
+		if (!*ptr)
+			largest = create.size;
+
+		munmap(ptr, create.size);
+		ptr = NULL;
+	}
+
+	longjmp(sigjmp, SIGABRT);
+}
+
 static void always_clear(int fd, int timeout)
 {
 	struct thread_clear arg = {
 		.fd = fd,
 		.timeout = timeout,
-		.max = intel_get_avail_ram_mb() << (20 - 12), /* in pages */
+		.max = estimate_largest_dumb_buffer(fd), /* in pages */
 	};
 	const int ncpus = sysconf(_SC_NPROCESSORS_ONLN);
 	unsigned long checked;
-- 
2.25.0