mm/gup_benchmark.c: time put_page()

We'd like to measure time to unpin user pages, so this adds a second
benchmark timer on put_page, separate from get_page.

Adding the field breaks this ioctl ABI, but should be okay since this an
in-tree kernel selftest.

[akpm@linux-foundation.org: add expansion to struct gup_benchmark for future use]
Link: http://lkml.kernel.org/r/20181010195605.10689-1-keith.busch@intel.com
Signed-off-by: Keith Busch <keith.busch@intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/gup_benchmark.c

@@ -8,11 +8,13 @@
 #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
 
 struct gup_benchmark {
-	__u64 delta_usec;
+	__u64 get_delta_usec;
+	__u64 put_delta_usec;
 	__u64 addr;
 	__u64 size;
 	__u32 nr_pages_per_call;
 	__u32 flags;
+	__u64 expansion[10];	/* For future use */
 };
 
 static int __gup_benchmark_ioctl(unsigned int cmd,
@@ -48,14 +50,17 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
 	}
 	end_time = ktime_get();
 
-	gup->delta_usec = ktime_us_delta(end_time, start_time);
+	gup->get_delta_usec = ktime_us_delta(end_time, start_time);
 	gup->size = addr - gup->addr;
 
+	start_time = ktime_get();
 	for (i = 0; i < nr_pages; i++) {
 		if (!pages[i])
 			break;
 		put_page(pages[i]);
 	}
+	end_time = ktime_get();
+	gup->put_delta_usec = ktime_us_delta(end_time, start_time);
 
 	kvfree(pages);
 	return 0;

tools/testing/selftests/vm/gup_benchmark.c

@@ -17,7 +17,8 @@
 #define GUP_FAST_BENCHMARK	_IOWR('g', 1, struct gup_benchmark)
 
 struct gup_benchmark {
-	__u64 delta_usec;
+	__u64 get_delta_usec;
+	__u64 put_delta_usec;
 	__u64 addr;
 	__u64 size;
 	__u32 nr_pages_per_call;
@@ -81,7 +82,8 @@ int main(int argc, char **argv)
 		if (ioctl(fd, GUP_FAST_BENCHMARK, &gup))
 			perror("ioctl"), exit(1);
 
-		printf("Time: %lld us", gup.delta_usec);
+		printf("Time: get:%lld put:%lld us", gup.get_delta_usec,
+			gup.put_delta_usec);
 		if (gup.size != size)
 			printf(", truncated (size: %lld)", gup.size);
 		printf("\n");