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. >>>> >>>> Another idea would be to add a field in indirect mbufs that stores >>>> the pointer to the "parent" mbuf. >>>> >>>> Regards, >>>> Olivier >>>>
