> -----Original Message----- > From: Olivier MATZ [mailto:olivier.matz at 6wind.com] > Sent: Wednesday, February 18, 2015 10:34 AM > To: Richardson, Bruce > Cc: Ananyev, Konstantin; dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH 2/2] Remove RTE_MBUF_REFCNT references > > Hi, > > On 02/18/2015 11:22 AM, Bruce Richardson wrote: > > On Wed, Feb 18, 2015 at 11:14:42AM +0100, Olivier MATZ wrote: > >> 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, my bad. > > How was this managed before, since refcnt field seems to be necessary in > > order > > to effectively manage indirect mbufs? Is this just the case that this is > > something > > that never worked and that needs to be solved, or is it something that was > > working that this patch will now break? > > This is something that never worked before: refcounts are not compatible > with reserving private data in mbufs. This patch does not change the > issue, it is still there. > > Before the patch, an application that wanted to reserve a private > data could disable refcounts at compile-time. > After the patch, the solution is just to avoid using refcounts.
I'd say avoid using mbuf_attach/detach. refcnt itself has nothing to do with that. I finally understood what you are talking about ... About private data - I suppose it is a matter of another patch. I still think it would be better to reserve private data space before mbuf, not after (at mbuf pool initialisation time). Then *BADDR* macros could be unaffected. Konstantin > > Regards, > Olivier >
