[dpdk-dev] memory barriers in rte_ring
olivier.matz at 6wind.com
Thu Mar 27 17:48:21 CET 2014
The commit 286bd05bf7  removed the memory barriers in the ring
functions. This patch is present in DPDK since version 1.4.0r0, so I
guess it does not cause any issue.
But after checking the excellent Linux kernel documentation about memory
barriers , I'm wondering why memory barriers would not be required in
To illustrate the previous behavior (before dpdk 1.4):
- move producer_head to reserve space in ring (atomically if
- write objects between producer_head and producer_tail
- wmb() to ensure that STORE operations are issued
- write producer_tail
- move consumer_head (atomically if multi consumers)
- rmb() to ensure that LOAD operations are issued: the read of
consumer_head must occur before the reading of objects ptrs.
In fact, rmb() is probably not needed here because knowing the
value of consumer_head is required before reading the objects
- read objects between consumer_head and consumer_tail
- write consumer_tail
The memory barriers have been removed, but in my understanding at least
the wmb() would be needed according to the generic memory barrier
documentation. Maybe this is not needed on newest Intel processors?
Could anyone from Intel enlight me on this?
Thanks & regards,
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