Re: [dpdk-dev] [PATCH] mbuf: decrease refcnt when detaching

[Hiroyuki MIKITA <h.mikita89@gmail.com>]

Hi Konstantin,

Now, the attach operation increases refcnt, but the detach does not decrease it.
I think both operations should affect refcnt or not.
Which design is intended?

In "6.7. Direct and Indirect Buffers" of Programmer's Guide,
it is mentioned that "...whenever an indirect buffer is attached to
the direct buffer,
the reference counter on the direct buffer is incremented.
Similarly, whenever the indirect buffer is detached,
the reference counter on the direct buffer is decremented."

Regards,
Hiroyuki

2016-05-16 9:05 GMT+09:00 Ananyev, Konstantin <konstantin.ananyev@intel.com>:
>
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Hiroyuki Mikita
>> Sent: Sunday, May 15, 2016 4:51 PM
>> To: olivier.matz@6wind.com
>> Cc: dev@dpdk.org
>> Subject: [dpdk-dev] [PATCH] mbuf: decrease refcnt when detaching
>>
>> The rte_pktmbuf_detach() function should decrease refcnt on a direct
>> buffer.
>
> Hmm, why is that?
> What's wrong with the current approach?
> Konstantin
>
>>
>> Signed-off-by: Hiroyuki Mikita <h.mikita89@gmail.com>
>> ---
>>  lib/librte_mbuf/rte_mbuf.h | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
>> index 529debb..3b117ca 100644
>> --- a/lib/librte_mbuf/rte_mbuf.h
>> +++ b/lib/librte_mbuf/rte_mbuf.h
>> @@ -1468,9 +1468,11 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *m)
>>   */
>>  static inline void rte_pktmbuf_detach(struct rte_mbuf *m)
>>  {
>> +     struct rte_mbuf *md = rte_mbuf_from_indirect(m);
>>       struct rte_mempool *mp = m->pool;
>>       uint32_t mbuf_size, buf_len, priv_size;
>>
>> +     rte_mbuf_refcnt_update(md, -1);
>>       priv_size = rte_pktmbuf_priv_size(mp);
>>       mbuf_size = sizeof(struct rte_mbuf) + priv_size;
>>       buf_len = rte_pktmbuf_data_room_size(mp);
>> @@ -1498,7 +1500,7 @@ __rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>>               if (RTE_MBUF_INDIRECT(m)) {
>>                       struct rte_mbuf *md = rte_mbuf_from_indirect(m);
>>                       rte_pktmbuf_detach(m);
>> -                     if (rte_mbuf_refcnt_update(md, -1) == 0)
>> +                     if (rte_mbuf_refcnt_read(md) == 0)
>>                               __rte_mbuf_raw_free(md);
>>               }
>>               return m;
>> --
>> 1.9.1
>