> -----Original Message----- > From: Olivier MATZ [mailto:olivier.matz at 6wind.com] > Sent: Wednesday, February 18, 2015 10:15 AM > To: Richardson, Bruce; Ananyev, Konstantin > Cc: dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH 2/2] Remove RTE_MBUF_REFCNT references > > On 02/18/2015 11:00 AM, Bruce Richardson wrote: > > 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? > > It's still used in __rte_pktmbuf_prefree_seg() to retrieve the > parent mbuf (direct) from the indirect mbuf beeing freed. >
Yes, if the INDIRECT flag is set. Though I still don't understand, what is the problem with these 2 macros with that patch? Why we need to replace it with something? What exactly you think will be broken? Konstantin > > > >>>> > >>>> Another idea would be to add a field in indirect mbufs that stores > >>>> the pointer to the "parent" mbuf. > >>>> > >>>> Regards, > >>>> Olivier > >>>>
