On Wed, Feb 18, 2015 at 09:48:58AM +0000, Ananyev, Konstantin wrote: > Hi lads, > > > -----Original Message----- > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Bruce Richardson > > Sent: Wednesday, February 18, 2015 9:36 AM > > To: Olivier MATZ > > Cc: dev at dpdk.org > > Subject: Re: [dpdk-dev] [PATCH 2/2] Remove RTE_MBUF_REFCNT references > > > > On Wed, Feb 18, 2015 at 10:16:56AM +0100, Olivier MATZ wrote: > > > Hi Sergio, > > > > > > On 02/16/2015 05:08 PM, Sergio Gonzalez Monroy wrote: > > > >This patch removes all references to RTE_MBUF_REFCNT, setting the refcnt > > > >field in the mbuf struct permanently. > > > > > > > >Signed-off-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy at > > > >intel.com> > > > > > > I think removing the refcount compile option goes in the right > > > direction. However, activating the refcount will break the applications > > > that reserve a private zone in mbufs. This is due to the macros > > > RTE_MBUF_TO_BADDR() and RTE_MBUF_FROM_BADDR() that suppose that > > > the beginning of the mbuf is 128 bytes (sizeof mbuf) before the > > > data buffer. > > > > > > > While I understand how the macros make certain assumptions, how does > > activating > > the refcnt specifically lead to the problems you describe? Could you explain > > that part in a bit more detail? > > > > Thanks, > > /Bruce > > > > Olivier, I also don't understand your concern here. > As I can see, that patch has nothing to do with RTE_MBUF_FROM_BADDR/ > RTE_MBUF_FROM_BADDR macros. > They are still there, for example rte_pktmbuf_detach() still uses it to > restore mbuf's buf_addr. > The only principal change here, is that we don't rely more on > RTE_MBUF_FROM_BADDR to determine, > Is that indirect mbuf or not. > Instead we use a special falg for that purpose: > > -#define RTE_MBUF_INDIRECT(mb) (RTE_MBUF_FROM_BADDR((mb)->buf_addr) != (mb)) > +#define RTE_MBUF_INDIRECT(mb) (mb->ol_flags & IND_ATTACHED_MBUF) > > BTW, Sergio as I said before, I think it should be: > #define RTE_MBUF_INDIRECT(mb) ((mb)->ol_flags & IND_ATTACHED_MBUF) > > Konstantin > > > > > For RTE_MBUF_TO_BADDR(), it's relatively easy to replace it. The > > > mbuf pool could store the size of the private size like it's done > > > for mbp_priv->mbuf_data_room_size. Using rte_mempool_from_obj(m) > > > or m->pool, we can retrieve the mbuf pool and this value, then > > > compute the buffer address.
Agreed, that makes sense. > > > > > > For RTE_MBUF_FROM_BADDR(), it's more complex. We could ensure that > > > a backpointer to the mbuf is always located before the data buffer, > > > but it looks difficult to do. On the other hand, with the proposed refcnt change Sergio proposes, we no longer use this macro in any of the built-in mbuf handling for freeing mbufs. Does this need to be solved at anything other than the application level? /Bruce > > > > > > Another idea would be to add a field in indirect mbufs that stores > > > the pointer to the "parent" mbuf. > > > > > > Regards, > > > Olivier > > >
