Re: [dpdk-dev] [PATCH v5 08/12] mbuf: fix clone support when application uses private mbuf data

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Konstantin,

On 04/21/2015 05:01 PM, Ananyev, Konstantin wrote:
> Hi Olivier,
>
>> -----Original Message-----
>> From: Olivier Matz [mailto:olivier.matz@6wind.com]
>> Sent: Tuesday, April 21, 2015 10:55 AM
>> To: dev@dpdk.org
>> Cc: Ananyev, Konstantin; zoltan.kiss@linaro.org; Richardson, Bruce; nhorman@tuxdriver.com; olivier.matz@6wind.com
>> Subject: [PATCH v5 08/12] mbuf: fix clone support when application uses private mbuf data
>>
>> Add a new private_size field in mbuf structure that should
>> be initialized at mbuf pool creation. This field contains the
>> size of the application private data in mbufs.
>>
>> Introduce new static inline functions rte_mbuf_from_indirect()
>> and rte_mbuf_to_baddr() to replace the existing macros, which
>> take the private size in account when attaching and detaching
>> mbufs.
>>
>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
>> Reviewed-by: Zoltan Kiss <zoltan.kiss@linaro.org>
>> ---
>>   examples/vhost/main.c      |  4 ++--
>>   lib/librte_mbuf/rte_mbuf.c |  2 +-
>>   lib/librte_mbuf/rte_mbuf.h | 59 +++++++++++++++++++++++++++++++---------------
>>   3 files changed, 43 insertions(+), 22 deletions(-)
>>
>> diff --git a/examples/vhost/main.c b/examples/vhost/main.c
>> index 22d6a4b..195d82f 100644
>> --- a/examples/vhost/main.c
>> +++ b/examples/vhost/main.c
>> @@ -138,7 +138,7 @@
>>   /* Number of descriptors per cacheline. */
>>   #define DESC_PER_CACHELINE (RTE_CACHE_LINE_SIZE / sizeof(struct vring_desc))
>>
>> -#define MBUF_EXT_MEM(mb)   (RTE_MBUF_FROM_BADDR((mb)->buf_addr) != (mb))
>> +#define MBUF_EXT_MEM(mb)   (rte_mbuf_from_indirect(mb) != (mb))
>>
>>   /* mask of enabled ports */
>>   static uint32_t enabled_port_mask = 0;
>> @@ -1549,7 +1549,7 @@ attach_rxmbuf_zcp(struct virtio_net *dev)
>>   static inline void pktmbuf_detach_zcp(struct rte_mbuf *m)
>>   {
>>   	const struct rte_mempool *mp = m->pool;
>> -	void *buf = RTE_MBUF_TO_BADDR(m);
>> +	void *buf = rte_mbuf_to_baddr(m);
>>   	uint32_t buf_ofs;
>>   	uint32_t buf_len = mp->elt_size - sizeof(*m);
>>   	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + sizeof(*m);
>> diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
>> index b013607..784ae8b 100644
>> --- a/lib/librte_mbuf/rte_mbuf.c
>> +++ b/lib/librte_mbuf/rte_mbuf.c
>> @@ -129,7 +129,7 @@ rte_pktmbuf_init(struct rte_mempool *mp,
>>
>>   	memset(m, 0, mp->elt_size);
>>
>> -	/* start of buffer is just after mbuf structure */
>> +	/* start of buffer is after mbuf structure and priv data */
>>   	m->buf_addr = (char *)m + mbuf_size;
>>   	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + mbuf_size;
>>   	m->buf_len = (uint16_t)buf_len;
>> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
>> index 42db8e3..5c01c5b 100644
>> --- a/lib/librte_mbuf/rte_mbuf.h
>> +++ b/lib/librte_mbuf/rte_mbuf.h
>> @@ -320,16 +320,40 @@ struct rte_mbuf {
>>   	};
>>   } __rte_cache_aligned;
>>
>> +static inline uint16_t rte_pktmbuf_priv_size(struct rte_mempool *mp);
>> +
>>   /**
>> - * Given the buf_addr returns the pointer to corresponding mbuf.
>> + * Return the mbuf owning the data buffer address of an indirect mbuf.
>> + *
>> + * @param mi
>> + *   The pointer to the indirect mbuf.
>> + * @return
>> + *   The address of the direct mbuf corresponding to buffer_addr.
>>    */
>> -#define RTE_MBUF_FROM_BADDR(ba)     (((struct rte_mbuf *)(ba)) - 1)
>> +static inline struct rte_mbuf *
>> +rte_mbuf_from_indirect(struct rte_mbuf *mi)
>> +{
>> +       struct rte_mbuf *md;
>> +       md = (struct rte_mbuf *)((char *)mi->buf_addr -
>> +	       sizeof(*mi) - rte_pktmbuf_priv_size(mi->pool));
>> +       return md;
>> +}
>
>
> Really puzzled, why do you remove prv_size from mbuf?
> Now if let say we attach mbuf (mi) with priv_size == X to mbuf (md) with priv_size == Y,
> then rte_mbuf_from_indirect(mi) would return: mi->buf_addr - 128 - X, while it should be: mi->buf_addr - 128 - Y.
>
> Another thing, rte_mbuf_from_indirect() and rte_mbuf_to_baddr() would probably become a bit slower -
> as another level of indirection is added.

You're right, I forgot this use case, it cannot work like this.
I think I will add a new test case, it will avoid me to break
it again in a version of the next patch series :)

Thanks,
Olivier



>
> Konstantin
>
>>
>>   /**
>> - * Given the pointer to mbuf returns an address where it's  buf_addr
>> - * should point to.
>> + * Return the buffer address embedded in the given mbuf.
>> + *
>> + * @param md
>> + *   The pointer to the mbuf.
>> + * @return
>> + *   The address of the data buffer owned by the mbuf.
>>    */
>> -#define RTE_MBUF_TO_BADDR(mb)       (((struct rte_mbuf *)(mb)) + 1)
>> +static inline char *
>> +rte_mbuf_to_baddr(struct rte_mbuf *md)
>> +{
>> +       char *buffer_addr;
>> +       buffer_addr = (char *)md + sizeof(*md) + rte_pktmbuf_priv_size(md->pool);
>> +       return buffer_addr;
>> +}
>>
>>   /**
>>    * Returns TRUE if given mbuf is indirect, or FALSE otherwise.
>> @@ -771,6 +795,7 @@ static inline struct rte_mbuf *rte_pktmbuf_alloc(struct rte_mempool *mp)
>>
>>   /**
>>    * Attach packet mbuf to another packet mbuf.
>> + *
>>    * After attachment we refer the mbuf we attached as 'indirect',
>>    * while mbuf we attached to as 'direct'.
>>    * Right now, not supported:
>> @@ -784,7 +809,6 @@ static inline struct rte_mbuf *rte_pktmbuf_alloc(struct rte_mempool *mp)
>>    * @param md
>>    *   The direct packet mbuf.
>>    */
>> -
>>   static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *md)
>>   {
>>   	RTE_MBUF_ASSERT(RTE_MBUF_DIRECT(md) &&
>> @@ -815,7 +839,8 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *md)
>>   }
>>
>>   /**
>> - * Detach an indirect packet mbuf -
>> + * Detach an indirect packet mbuf.
>> + *
>>    *  - restore original mbuf address and length values.
>>    *  - reset pktmbuf data and data_len to their default values.
>>    *  All other fields of the given packet mbuf will be left intact.
>> @@ -823,22 +848,18 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *md)
>>    * @param m
>>    *   The indirect attached packet mbuf.
>>    */
>> -
>>   static inline void rte_pktmbuf_detach(struct rte_mbuf *m)
>>   {
>> -	const struct rte_mempool *mp = m->pool;
>> -	void *buf = RTE_MBUF_TO_BADDR(m);
>> -	uint32_t buf_len = mp->elt_size - sizeof(*m);
>> -	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + sizeof (*m);
>> +	struct rte_mempool *mp = m->pool;
>> +	uint32_t mbuf_size, buf_len;
>>
>> -	m->buf_addr = buf;
>> +	mbuf_size = sizeof(struct rte_mbuf) + rte_pktmbuf_priv_size(mp);
>> +	buf_len = rte_pktmbuf_data_room_size(mp);
>> +	m->buf_addr = rte_mbuf_to_baddr(m);
>> +	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + mbuf_size;
>>   	m->buf_len = (uint16_t)buf_len;
>> -
>> -	m->data_off = (RTE_PKTMBUF_HEADROOM <= m->buf_len) ?
>> -			RTE_PKTMBUF_HEADROOM : m->buf_len;
>> -
>> +	m->data_off = RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
>>   	m->data_len = 0;
>> -
>>   	m->ol_flags = 0;
>>   }
>>
>> @@ -867,7 +888,7 @@ __rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>>   		 *  - free attached mbuf segment
>>   		 */
>>   		if (RTE_MBUF_INDIRECT(m)) {
>> -			struct rte_mbuf *md = RTE_MBUF_FROM_BADDR(m->buf_addr);
>> +			struct rte_mbuf *md = rte_mbuf_from_indirect(m);
>>   			rte_pktmbuf_detach(m);
>>   			if (rte_mbuf_refcnt_update(md, -1) == 0)
>>   				__rte_mbuf_raw_free(md);
>> --
>> 2.1.4
>