[dpdk-dev] [RFC PATCH v2] vhost: Add VHOST PMD

Bruce Richardson bruce.richardson at intel.com
Wed Oct 21 12:09:39 CEST 2015


On Wed, Oct 21, 2015 at 01:30:54PM +0900, Tetsuya Mukawa wrote:
> On 2015/10/20 23:13, Loftus, Ciara wrote:
> >
> > I see that af_packet also frees the mbuf. I've checked the ixgbe and ring pmds though and they don't seem to free the buffers, although I may have missed something, the code for these is rather large and I am unfamiliar with most of it. If I am correct though, should this behaviour vary from PMD to PMD I wonder?
> 
> I guess ring PMD is something special.
> Because we don't want to copy data with this PMD, RX function doesn't
> allocate buffers, also TX function doesn't free buffers.
> But other normal PMD will allocate buffers when RX is called, and free
> buffers when TX is called.
> 

Yes, this is correct. Ring pmd is the exception since it automatically recycles
buffers, and so does not need to alloc/free mbufs. (ixgbe frees the buffers 
post-TX as part of the TX ring cleanup)

/Bruce



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