From 5c1a533e86fc451f2669fef3450a138410e0f221 Mon Sep 17 00:00:00 2001 From: Feifei Wang Date: Tue, 18 May 2021 16:50:58 +0800 Subject: [PATCH] net/mlx5: remove barrier for memory region cache 'dev_gen' is a variable to trigger all cores to flush their local caches once the global MR cache has been rebuilt. This is due to MR cache's R/W lock can maintain synchronization between threads: 1. dev_gen and global cache updating ordering inside the lock protected section does not matter. Because other threads cannot take the lock until global cache has been updated. Thus, in out of order platform, even if other agents firstly observe updated dev_gen but global does not update, they also have to wait the lock. As a result, it is unnecessary to add a wmb between global cache rebuilding and updating the dev_gen to keep the memory store order. 2. Store-Release of unlock provides the implicit wmb at the level visible by software. This makes 'rebuilding global cache' and 'updating dev_gen' be observed before local_cache starts to be updated by other agents. Thus, wmb after 'updating dev_gen' can be removed. Suggested-by: Ruifeng Wang Signed-off-by: Feifei Wang Reviewed-by: Ruifeng Wang Acked-by: Viacheslav Ovsiienko --- drivers/net/mlx5/mlx5_mr.c | 22 ++++++---------------- 1 file changed, 6 insertions(+), 16 deletions(-) diff --git a/drivers/net/mlx5/mlx5_mr.c b/drivers/net/mlx5/mlx5_mr.c index e791b6338d..0c5403e493 100644 --- a/drivers/net/mlx5/mlx5_mr.c +++ b/drivers/net/mlx5/mlx5_mr.c @@ -107,18 +107,13 @@ mlx5_mr_mem_event_free_cb(struct mlx5_dev_ctx_shared *sh, if (rebuild) { mlx5_mr_rebuild_cache(&sh->share_cache); /* - * Flush local caches by propagating invalidation across cores. - * rte_smp_wmb() is enough to synchronize this event. If one of - * freed memsegs is seen by other core, that means the memseg - * has been allocated by allocator, which will come after this - * free call. Therefore, this store instruction (incrementing - * generation below) will be guaranteed to be seen by other core - * before the core sees the newly allocated memory. + * No explicit wmb is needed after updating dev_gen due to + * store-release ordering in unlock that provides the + * implicit barrier at the software visible level. */ ++sh->share_cache.dev_gen; DRV_LOG(DEBUG, "broadcasting local cache flush, gen=%d", sh->share_cache.dev_gen); - rte_smp_wmb(); } rte_rwlock_write_unlock(&sh->share_cache.rwlock); } @@ -411,18 +406,13 @@ mlx5_dma_unmap(struct rte_pci_device *pdev, void *addr, (void *)mr); mlx5_mr_rebuild_cache(&sh->share_cache); /* - * Flush local caches by propagating invalidation across cores. - * rte_smp_wmb() is enough to synchronize this event. If one of - * freed memsegs is seen by other core, that means the memseg - * has been allocated by allocator, which will come after this - * free call. Therefore, this store instruction (incrementing - * generation below) will be guaranteed to be seen by other core - * before the core sees the newly allocated memory. + * No explicit wmb is needed after updating dev_gen due to + * store-release ordering in unlock that provides the + * implicit barrier at the software visible level. */ ++sh->share_cache.dev_gen; DRV_LOG(DEBUG, "broadcasting local cache flush, gen=%d", sh->share_cache.dev_gen); - rte_smp_wmb(); rte_rwlock_read_unlock(&sh->share_cache.rwlock); return 0; } -- 2.20.1