[PATCH v3 09/10] iov_iter: Add kunit to benchmark decanting of xarray to bvec

David Howells
2023-09-22T11:31:22Z

Add a kunit test to benchmark an xarray containing 256MiB of data getting
decanted into 256-page BVEC iterators that get copied from - modelling
bufferage being drawn from the pagecache and batched up for I/O.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christoph Hellwig <hch@lst.de>
cc: Christian Brauner <brauner@kernel.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: David Hildenbrand <david@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: Brendan Higgins <brendanhiggins@google.com>
cc: David Gow <davidgow@google.com>
cc: linux-kselftest@vger.kernel.org
cc: kunit-dev@googlegroups.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
lib/kunit_iov_iter.c | 87 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 87 insertions(+)

diff --git a/lib/kunit_iov_iter.c b/lib/kunit_iov_iter.c
index 1a43e9518a63..2fbe6f2afb26 100644
--- a/lib/kunit_iov_iter.c
+++ b/lib/kunit_iov_iter.c
@@ -1509,6 +1509,92 @@ static void __init iov_kunit_benchmark_xarray(struct kunit *test)
KUNIT_SUCCEED();
}

+/*
+ * Time copying 256MiB through an ITER_XARRAY, decanting it to ITER_BVECs.
+ */
+static void __init iov_kunit_benchmark_xarray_to_bvec(struct kunit *test)
+{
+ struct iov_iter xiter;
+ struct xarray *xarray;
+ struct page *page;
+ 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;
+
+ /* Allocate a page and tile it repeatedly in the buffer. */
+ page = alloc_page(GFP_KERNEL);
+ KUNIT_ASSERT_NOT_NULL(test, page);
+ kunit_add_action_or_reset(test, iov_kunit_free_page, page);
+
+ xarray = iov_kunit_create_xarray(test);
+
+ for (i = 0; i < npages; i++) {
+ void *x = xa_store(xarray, i, page, GFP_KERNEL);
+
+ KUNIT_ASSERT_FALSE(test, xa_is_err(x));
+ }
+
+ /* 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 BVECs decanted from an XARRAY:\n");
+ for (i = 0; i < IOV_KUNIT_NR_SAMPLES; i++) {
+ size = 256 * 1024 * 1024;
+ iov_iter_xarray(&xiter, ITER_SOURCE, xarray, 0, size);
+ a = ktime_get_real();
+
+ do {
+ struct iov_iter biter;
+ struct bio_vec *bvec;
+ struct page **pages;
+ size_t req, part, offset0, got;
+ int j;
+
+ npages = 256;
+ req = min_t(size_t, size, npages * PAGE_SIZE);
+ bvec = kunit_kmalloc_array(test, npages, sizeof(bvec[0]), GFP_KERNEL);
+ KUNIT_ASSERT_NOT_NULL(test, bvec);
+
+ pages = (void *)bvec + array_size(npages, sizeof(bvec[0])) -
+ array_size(npages, sizeof(*pages));
+
+ part = iov_iter_extract_pages(&xiter, &pages, req,
+ npages, 0, &offset0);
+ KUNIT_EXPECT_NE(test, part, 0);
+ KUNIT_EXPECT_GT(test, part, 0);
+
+ j = 0;
+ got = part;
+ do {
+ size_t chunk = min_t(size_t, got, PAGE_SIZE - offset0);
+
+ bvec_set_page(&bvec[j++], page, chunk, offset0);
+ offset0 = 0;
+ got -= chunk;
+ } while (got > 0);
+
+ iov_iter_bvec(&biter, ITER_SOURCE, bvec, j, part);
+ copied = copy_from_iter(scratch, part, &biter);
+ KUNIT_EXPECT_EQ(test, copied, part);
+ size -= copied;
+ if (test->status == KUNIT_FAILURE)
+ break;
+ } while (size > 0);
+
+ b = ktime_get_real();
+ samples[i] = ktime_to_us(ktime_sub(b, a));
+ if (test->status == KUNIT_FAILURE)
+ break;
+ }
+
+ iov_kunit_benchmark_print_stats(test, samples);
+ KUNIT_SUCCEED();
+}
+
static struct kunit_case __refdata iov_kunit_cases[] = {
KUNIT_CASE(iov_kunit_copy_to_ubuf),
KUNIT_CASE(iov_kunit_copy_from_ubuf),
@@ -1529,6 +1615,7 @@ static struct kunit_case __refdata iov_kunit_cases[] = {
KUNIT_CASE(iov_kunit_benchmark_bvec),
KUNIT_CASE(iov_kunit_benchmark_bvec_split),
KUNIT_CASE(iov_kunit_benchmark_xarray),
+ KUNIT_CASE(iov_kunit_benchmark_xarray_to_bvec),
{}
};