On Wed, Jan 28, 2026 at 8:59 AM Stephen Hemminger <[email protected]> wrote: > > On Wed, 28 Jan 2026 01:36:04 -0800 > [email protected] wrote: > > > +/** > > + * Read tp_status from packet mmap ring. Matches kernel's READ_ONCE() with > > smp_rmb() > > + * ordering in af_packet.c __packet_get_status. > > + */ > > +static inline uint32_t > > +tpacket_read_status(const volatile void *tp_status) > > +{ > > + rte_smp_rmb(); > > + return *((const volatile unaligned_uint32_t *)tp_status); > > +} > > Wouldn't rte_compiler_barrier() be better choice here. > You are really only trying to keep compiler from optimzing the access. > > And tp_status is aligned in ring isn't it?
The current approach replicates __packet_set_status and __packet_get_status [1] in the kernel which use the same barriers (WRITE_ONCE calls __write_once_size [2] which does a volatile cast). dpdk's rte_smp_rmb and rte_smp_wmb on x86 are just rte_compiler_barrier [3] but on arm it's different [4]. [1] https://github.com/torvalds/linux/blob/v6.18/net/packet/af_packet.c#L399-L451 [2] https://github.com/torvalds/linux/blob/v6.18/tools/include/linux/compiler.h#L194 [3] https://github.com/DPDK/dpdk/blob/v25.11/lib/eal/x86/include/rte_atomic.h#L26-L28 [4] https://github.com/DPDK/dpdk/blob/v25.11/lib/eal/arm/include/rte_atomic_64.h#L29-L31
