[RFC PATCH 9/9] iov_iter: Add benchmarking kunit tests for UBUF/IOVEC

[David Howells]

Add kunit tests to benchmark 256MiB copies to a UBUF iterator and an IOVEC
iterator.  This attaches a userspace VM with a mapped file in it
temporarily to the test thread.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
cc: Christoph Hellwig <hch@xxxxxx>
cc: Christian Brauner <brauner@xxxxxxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
cc: David Hildenbrand <david@xxxxxxxxxx>
cc: John Hubbard <jhubbard@xxxxxxxxxx>
cc: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
cc: David Gow <davidgow@xxxxxxxxxx>
cc: linux-kselftest@xxxxxxxxxxxxxxx
cc: kunit-dev@xxxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
 lib/kunit_iov_iter.c | 85 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)

diff --git a/lib/kunit_iov_iter.c b/lib/kunit_iov_iter.c
index f8d0cd6a2923..cc9c64663a73 100644
--- a/lib/kunit_iov_iter.c
+++ b/lib/kunit_iov_iter.c
@@ -1304,6 +1304,89 @@ static void *__init iov_kunit_create_source(struct kunit *test, size_t npages)
 	return scratch;
 }
 
+/*
+ * Time copying 256MiB through an ITER_UBUF.
+ */
+static void __init iov_kunit_benchmark_ubuf(struct kunit *test)
+{
+	struct iov_iter iter;
+	unsigned int samples[IOV_KUNIT_NR_SAMPLES];
+	ktime_t a, b;
+	ssize_t copied;
+	size_t size = 256 * 1024 * 1024, npages = size / PAGE_SIZE;
+	void *scratch;
+	int i;
+	u8 __user *buffer;
+
+	/* Allocate a huge buffer and populate it with pages. */
+	buffer = iov_kunit_create_user_buf(test, npages, NULL);
+
+	/* Create a single large buffer to copy to/from. */
+	scratch = iov_kunit_create_source(test, npages);
+
+	/* Perform and time a bunch of copies. */
+	kunit_info(test, "Benchmarking copy_to_iter() over UBUF:\n");
+	for (i = 0; i < IOV_KUNIT_NR_SAMPLES; i++) {
+		iov_iter_ubuf(&iter, ITER_DEST, buffer, size);
+
+		a = ktime_get_real();
+		copied = copy_to_iter(scratch, size, &iter);
+		b = ktime_get_real();
+		KUNIT_EXPECT_EQ(test, copied, size);
+		samples[i] = ktime_to_us(ktime_sub(b, a));
+	}
+
+	iov_kunit_benchmark_print_stats(test, samples);
+	KUNIT_SUCCEED();
+}
+
+/*
+ * Time copying 256MiB through an ITER_IOVEC.
+ */
+static void __init iov_kunit_benchmark_iovec(struct kunit *test)
+{
+	struct iov_iter iter;
+	struct iovec iov[8];
+	unsigned int samples[IOV_KUNIT_NR_SAMPLES];
+	ktime_t a, b;
+	ssize_t copied;
+	size_t size = 256 * 1024 * 1024, npages = size / PAGE_SIZE, part;
+	void *scratch;
+	int i;
+	u8 __user *buffer;
+
+	/* Allocate a huge buffer and populate it with pages. */
+	buffer = iov_kunit_create_user_buf(test, npages, NULL);
+
+	/* Create a single large buffer to copy to/from. */
+	scratch = iov_kunit_create_source(test, npages);
+
+	/* Split the target over a number of iovecs */
+	copied = 0;
+	for (i = 0; i < ARRAY_SIZE(iov); i++) {
+		part = size / ARRAY_SIZE(iov);
+		iov[i].iov_base = buffer + copied;
+		iov[i].iov_len = part;
+		copied += part;
+	}
+	iov[i - 1].iov_len += size - part;
+
+	/* Perform and time a bunch of copies. */
+	kunit_info(test, "Benchmarking copy_to_iter() over IOVEC:\n");
+	for (i = 0; i < IOV_KUNIT_NR_SAMPLES; i++) {
+		iov_iter_init(&iter, ITER_DEST, iov, ARRAY_SIZE(iov), size);
+
+		a = ktime_get_real();
+		copied = copy_to_iter(scratch, size, &iter);
+		b = ktime_get_real();
+		KUNIT_EXPECT_EQ(test, copied, size);
+		samples[i] = ktime_to_us(ktime_sub(b, a));
+	}
+
+	iov_kunit_benchmark_print_stats(test, samples);
+	KUNIT_SUCCEED();
+}
+
 /*
  * Time copying 256MiB through an ITER_KVEC.
  */
@@ -1504,6 +1587,8 @@ static struct kunit_case __refdata iov_kunit_cases[] = {
 	KUNIT_CASE(iov_kunit_extract_pages_kvec),
 	KUNIT_CASE(iov_kunit_extract_pages_bvec),
 	KUNIT_CASE(iov_kunit_extract_pages_xarray),
+	KUNIT_CASE(iov_kunit_benchmark_ubuf),
+	KUNIT_CASE(iov_kunit_benchmark_iovec),
 	KUNIT_CASE(iov_kunit_benchmark_kvec),
 	KUNIT_CASE(iov_kunit_benchmark_bvec),
 	KUNIT_CASE(iov_kunit_benchmark_bvec_split),