On Tue, Jul 08, 2025 at 02:46:04PM +0200, David Marchand wrote:
> On Tue, Jul 8, 2025 at 2:44 PM Bruce Richardson
> <bruce.richard...@intel.com> wrote:
> >
> > On Tue, Jul 08, 2025 at 02:28:16PM +0200, David Marchand wrote:
> > > Content (param[]) of received multiprocess messages are aligned with
> > > a 4 bytes constraint.
> > >
> > > Before patch:
> > > struct mp_msg_internal {
> > > int type; /* 0
> > > 4 */
> > > struct rte_mp_msg {
> > > char name[64]; /* 4
> > > 64 */
> > > /* --- cacheline 1 boundary (64 bytes) was 4 bytes ago --- */
> > > int len_param; /* 68
> > > 4 */
> > > int num_fds; /* 72
> > > 4 */
> > > /* typedef uint8_t -> __uint8_t */ unsigned char param[256]; /* 76
> > > 256 */
> > > /* --- cacheline 5 boundary (320 bytes) was 12 bytes ago --- */
> > > int fds[253]; /* 332
> > > 1012 */
> > > } msg; /* 4
> > > 1340 */
> > >
> > > /* size: 1344, cachelines: 21, members: 2 */
> > > };
> > >
> > > This results in many unaligned accesses for multiprocess malloc requests.
> > >
> > > Examples:
> > > ../lib/eal/common/malloc_mp.c:308:32: runtime error:
> > > member access within misaligned address 0x7f7b35df4684 for type
> > > 'const struct malloc_mp_req', which requires 8 byte alignment
> > >
> > > ../lib/eal/common/malloc_mp.c:158:9: runtime error:
> > > member access within misaligned address 0x7f36a535bb5c for type
> > > 'const struct malloc_mp_req', which requires 8 byte alignment
> > >
> > > ../lib/eal/common/malloc_mp.c:171:8: runtime error:
> > > member access within misaligned address 0x7f4ba65f296c for type
> > > 'struct malloc_mp_req', which requires 8 byte alignment
> > >
> > > Signed-off-by: David Marchand <david.march...@redhat.com>
> > > ---
> > > lib/eal/common/eal_common_proc.c | 2 +-
> > > lib/eal/common/malloc_mp.c | 18 +++++++++---------
> > > 2 files changed, 10 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/lib/eal/common/eal_common_proc.c
> > > b/lib/eal/common/eal_common_proc.c
> > > index 0dea787e38..3846c7178d 100644
> > > --- a/lib/eal/common/eal_common_proc.c
> > > +++ b/lib/eal/common/eal_common_proc.c
> > > @@ -62,7 +62,7 @@ enum mp_type {
> > >
> > > struct mp_msg_internal {
> > > int type;
> > > - struct rte_mp_msg msg;
> > > + alignas(8) struct rte_mp_msg msg;
> > > };
> > >
> > > struct async_request_param {
> > > diff --git a/lib/eal/common/malloc_mp.c b/lib/eal/common/malloc_mp.c
> > > index 9765277f5d..000c7f6b47 100644
> > > --- a/lib/eal/common/malloc_mp.c
> > > +++ b/lib/eal/common/malloc_mp.c
> > > @@ -148,7 +148,7 @@ get_unique_id(void)
> > > static int
> > > handle_sync(const struct rte_mp_msg *msg, const void *peer)
> > > {
> > > - struct rte_mp_msg reply;
> > > + alignas(8) struct rte_mp_msg reply;
> > > const struct malloc_mp_req *req =
> > > (const struct malloc_mp_req *)msg->param;
> >
> > This patch seems to have a lot of these definitions with alignas added to
> > them. Would it be simpler just to put the alignas inside the rte_mp_msg
> > definition?
> >
> > More specifically, if its the "uint8_t param" element that needs alignment,
> > how about changing that specific field to make it aligned?
>
> We could probably enhance this, but I expect this breaks ABI.
>
Is the multi-process message type part of the public ABI? I don't believe
we ever guaranteed multiprocess support working across versions of DPDK.
/Bruce
