+CC Gavin, reviewed the test case > From: Ruifeng Wang [mailto:ruifeng.w...@arm.com] > Sent: Friday, 10 November 2023 09.40 > > On 2023/11/4 8:04 AM, Morten Brørup wrote: > > I have for a long time now wondered why the ring functions for > enqueue/dequeue of 64-bit objects supports unaligned addresses, and now > I finally found the patch introducing it. > > > >> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Phil Yang > >> Sent: Monday, 9 March 2020 18.20 > >> > >> The 32-bit arm machine doesn't support unaligned memory access. It > >> will cause a bus error on aarch32 with the custom element size ring. > >> > >> Thread 1 "test" received signal SIGBUS, Bus error. > >> __rte_ring_enqueue_elems_64 (n=1, obj_table=0xf5edfe41, prod_head=0, > \ > >> r=0xf5edfb80) at /build/dpdk/build/include/rte_ring_elem.h:177 > >> 177 ring[idx++] = obj[i++]; > > > > Which test is this? Why is it using an unaligned array of 64-bit > objects? (Notice that obj_table=0xf5edfe41.) > > The test case is: > https://elixir.bootlin.com/dpdk/latest/source/app/test/test_ring.c#L112 > 1 > This case deliberately use unaligned objects.
Thank you, Ruifeng. Honnappa, I see you signed off on the patch introducing the test for unaligned objects: http://git.dpdk.org/dpdk/commit/app/test/test_ring.c?id=a9fe152363e283d4c590ab8e8d51396f2ffab9ff What was the rationale behind testing support for unaligned object pointers? Did any applications/customers use unaligned object pointers, or is it a purely academic test case? > > > > > Nobody in their right mind would use an unaligned array of 64-bit > objects. You can only create such an array if you force the compiler to > prevent automatic alignment! And all the functions in your application > using this array would also need to support unaligned addressing of > these objects. > > > > This seems extremely exotic, and not something any real application > would do! > > > > I would like to revert this patch for performance reasons. I could add an RTE_ASSERT() to verify that the pointer is aligned, for debugging purposes. > > > >> > >> Fixes: cc4b218790f6 ("ring: support configurable element size") > >> > >> Signed-off-by: Phil Yang <phil.y...@arm.com> > >> Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com> > >> Reviewed-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com> > >> --- > >> lib/librte_ring/rte_ring_elem.h | 4 ++-- > >> 1 file changed, 2 insertions(+), 2 deletions(-) > >> > >> diff --git a/lib/librte_ring/rte_ring_elem.h > >> b/lib/librte_ring/rte_ring_elem.h > >> index 3976757..663addc 100644 > >> --- a/lib/librte_ring/rte_ring_elem.h > >> +++ b/lib/librte_ring/rte_ring_elem.h > >> @@ -160,7 +160,7 @@ __rte_ring_enqueue_elems_64(struct rte_ring *r, > >> uint32_t prod_head, > >> const uint32_t size = r->size; > >> uint32_t idx = prod_head & r->mask; > >> uint64_t *ring = (uint64_t *)&r[1]; > >> - const uint64_t *obj = (const uint64_t *)obj_table; > >> + const unaligned_uint64_t *obj = (const unaligned_uint64_t > >> *)obj_table; > >> if (likely(idx + n < size)) { > >> for (i = 0; i < (n & ~0x3); i += 4, idx += 4) { > >> ring[idx] = obj[i]; > >> @@ -294,7 +294,7 @@ __rte_ring_dequeue_elems_64(struct rte_ring *r, > >> uint32_t prod_head, > >> const uint32_t size = r->size; > >> uint32_t idx = prod_head & r->mask; > >> uint64_t *ring = (uint64_t *)&r[1]; > >> - uint64_t *obj = (uint64_t *)obj_table; > >> + unaligned_uint64_t *obj = (unaligned_uint64_t *)obj_table; > >> if (likely(idx + n < size)) { > >> for (i = 0; i < (n & ~0x3); i += 4, idx += 4) { > >> obj[i] = ring[idx]; > >> -- > >> 2.7.4 > >> > > > > References: > > > https://git.dpdk.org/dpdk/commit/lib/librte_ring/rte_ring_elem.h?id=3ba > 51478a3ab3132c33effc8b132641233275b36 > > https://patchwork.dpdk.org/project/dpdk/patch/1583774395-10233-1-git- > send-email-phil.y...@arm.com/ > >
