The branch main has been updated by andrew: URL: https://cgit.FreeBSD.org/src/commit/?id=7eb0fffc7792bc294d6b86546a3923e2e2f83f8a
commit 7eb0fffc7792bc294d6b86546a3923e2e2f83f8a Author: Andrew Turner <[email protected]> AuthorDate: 2024-08-19 09:07:10 +0000 Commit: Andrew Turner <[email protected]> CommitDate: 2024-08-19 10:53:11 +0000 buf_ring: Remove old arm-only dequeue code In the single consumer dequeue the consumer thread controls br_cons_head. As such no ordering between this and other data are required. Reviewed by: alc, imp, kib, markj Sponsored by: Arm Ltd Differential Revision: https://reviews.freebsd.org/D46153 --- sys/sys/buf_ring.h | 29 ----------------------------- 1 file changed, 29 deletions(-) diff --git a/sys/sys/buf_ring.h b/sys/sys/buf_ring.h index 9aeb5aa19fa8..ad463fba27cb 100644 --- a/sys/sys/buf_ring.h +++ b/sys/sys/buf_ring.h @@ -177,37 +177,8 @@ buf_ring_dequeue_sc(struct buf_ring *br) uint32_t prod_tail, mask; void *buf; - /* - * This is a workaround to allow using buf_ring on ARM and ARM64. - * ARM64TODO: Fix buf_ring in a generic way. - * REMARKS: It is suspected that br_cons_head does not require - * load_acq operation, but this change was extensively tested - * and confirmed it's working. To be reviewed once again in - * FreeBSD-12. - * - * Preventing following situation: - - * Core(0) - buf_ring_enqueue() Core(1) - buf_ring_dequeue_sc() - * ----------------------------------------- ---------------------------------------------- - * - * cons_head = br->br_cons_head; - * atomic_cmpset_acq_32(&br->br_prod_head, ...)); - * buf = br->br_ring[cons_head]; <see <1>> - * br->br_ring[prod_head] = buf; - * atomic_store_rel_32(&br->br_prod_tail, ...); - * prod_tail = br->br_prod_tail; - * if (cons_head == prod_tail) - * return (NULL); - * <condition is false and code uses invalid(old) buf>` - * - * <1> Load (on core 1) from br->br_ring[cons_head] can be reordered (speculative readed) by CPU. - */ mask = br->br_cons_mask; -#if defined(__arm__) || defined(__aarch64__) - cons_head = atomic_load_acq_32(&br->br_cons_head); -#else cons_head = br->br_cons_head; -#endif prod_tail = atomic_load_acq_32(&br->br_prod_tail); cons_next = cons_head + 1;
