Hi Bruce, I'm Hanoch from Cisco Systems works for the https://github.com/cisco-system-traffic-generator/trex-core traffic generator project.
While upgrading from DPDK 1.8 to 2.2 Ido found that the following commit creates a mbuf corruption and result in Tx hang commit f20b50b946da9070d21e392e4dbc7d9f68bc983e Author: Olivier Matz <olivier.matz at 6wind.com> Date: Mon Jun 8 16:57:22 2015 +0200 Looking at the change it is clear why there is an issue, wanted to get your input. Init ----- alloc const mbuf ==> mbuf-a (ref=1) Simple case that works --------------------- thread 1 , tx: alloc-mbuf->attach(mbuf-a) (ref=2) inc- non atomic thread 1 , tx: alloc-mbuf->attach(mbuf-a) (ref32) inc- atomic thread 1 , drv : free() (ref=2) dec- atomic thread 1 , drv : free() (ref=3) dec - non atomic Simple case that does not work --------------------- Both do that in parallel thread 2 tx : alloc-mbuf->attach(mbuf-a) (ref=2) inc- non atomic thread 1 tx : alloc-mbuf->attach(mbuf-a) (ref=2) inc- non atomic ==> ref in corrupted thread 1 drv : free() (ref=0) - free thread 1 drv : free() (ref=-1) - ??? Just as a side note that in our case we could benefit from this optimization by making a small change in our code, as our common case could be alloc/free of simple mbuf and in such scenario there is no atomic operation in both cases. But I think the general case is broken. Could you explain what was your use case or this optimization? Is it a valid example the aforementioned example thanks, Hanoh Cisco Systems On Mon, Jun 08, 2015 at 04:57:22PM +0200, Olivier Matz wrote: > In __rte_pktmbuf_prefree_seg(), there was an optimization to avoid using > a costly atomic operation when updating the mbuf reference counter if > its value is 1. Indeed, it means that we are the only owner of the mbuf, > and therefore nobody can change it at the same time. > > We can generalize this optimization directly in rte_mbuf_refcnt_update() > so the other callers of this function, like rte_pktmbuf_attach(), can > also take advantage of this optimization. > > Signed-off-by: Olivier Matz <olivier.matz at > 6wind.com<http://dpdk.org/ml/listinfo/dev>> Acked-by: Bruce Richardson <bruce.richardson at intel.com<http://dpdk.org/ml/listinfo/dev>> Hanoh
