d/numam-dpdk
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

net/mlx5: remove barrier for memory region cache

Browse Source 
'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 <ruifeng.wang@arm.com>
Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
This commit is contained in:
Feifei Wang 2021-05-18 16:50:58 +08:00 committed by Raslan Darawsheh
parent f0f7c557f3
commit 5c1a533e86
1 changed files with 6 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
drivers/net/mlx5/mlx5_mr.c
View File

@ -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;
}