Re: [dpdk-dev] [PATCH v3 1/5] mbuf: fix clone support when application uses private mbuf data

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Olivier,

> -----Original Message-----
> From: Olivier MATZ [mailto:olivier.matz@6wind.com]
> Sent: Monday, April 06, 2015 10:50 PM
> To: Ananyev, Konstantin; dev@dpdk.org
> Cc: zoltan.kiss@linaro.org; Richardson, Bruce
> Subject: Re: [PATCH v3 1/5] mbuf: fix clone support when application uses private mbuf data
> 
> Hi Konstantin,
> 
> Thanks for your comments.
> 
> On 04/02/2015 07:21 PM, Ananyev, Konstantin wrote:
> > Hi Olivier,
> >
> >> -----Original Message-----
> >> From: Olivier Matz [mailto:olivier.matz@6wind.com]
> >> Sent: Tuesday, March 31, 2015 8:23 PM
> >> To: dev@dpdk.org
> >> Cc: Ananyev, Konstantin; zoltan.kiss@linaro.org; Richardson, Bruce; Olivier Matz
> >> Subject: [PATCH v3 1/5] mbuf: fix clone support when application uses private mbuf data
> >>
> >> From: Olivier Matz <olivier.matz@6wind.com>
> >>
> >> 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>
> >> ---
> >>  app/test-pmd/testpmd.c     |  1 +
> >>  examples/vhost/main.c      |  4 +--
> >>  lib/librte_mbuf/rte_mbuf.c |  1 +
> >>  lib/librte_mbuf/rte_mbuf.h | 77 +++++++++++++++++++++++++++++++++++-----------
> >>  4 files changed, 63 insertions(+), 20 deletions(-)
> >>
> >> diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
> >> index 3057791..c5a195a 100644
> >> --- a/app/test-pmd/testpmd.c
> >> +++ b/app/test-pmd/testpmd.c
> >> @@ -425,6 +425,7 @@ testpmd_mbuf_ctor(struct rte_mempool *mp,
> >>  	mb->tx_offload   = 0;
> >>  	mb->vlan_tci     = 0;
> >>  	mb->hash.rss     = 0;
> >> +	mb->priv_size    = 0;
> >>  }
> >>
> >>  static void
> >> diff --git a/examples/vhost/main.c b/examples/vhost/main.c
> >> index c3fcb80..e44e82f 100644
> >> --- a/examples/vhost/main.c
> >> +++ b/examples/vhost/main.c
> >> @@ -139,7 +139,7 @@
> >>  /* 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;
> >> @@ -1550,7 +1550,7 @@ 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 526b18d..e095999 100644
> >> --- a/lib/librte_mbuf/rte_mbuf.c
> >> +++ b/lib/librte_mbuf/rte_mbuf.c
> >> @@ -125,6 +125,7 @@ rte_pktmbuf_init(struct rte_mempool *mp,
> >>  	m->pool = mp;
> >>  	m->nb_segs = 1;
> >>  	m->port = 0xff;
> >> +	m->priv_size = 0;
> >
> > Why it is 0?
> > Shouldn't it be the same calulations as in detach() below:
> > m->priv_size = /*get private size from mempool private*/;
> > m->buf_addr = (char *)m + sizeof(struct rte_mbuf) + m->priv_size;
> > m->buf_len = mp->elt_size - sizeof(struct rte_mbuf) - m->priv_size;
> > ?
> 
> It's 0 because we also have in the function (not visible in the
> patch):
> 
>   m->buf_addr = (char *)m + sizeof(struct rte_mbuf);

Yep, that's why as I wrote above, I think we need to setup here all 3 fields:
priv_size, buf_addr, buf_len exactly in the same way as in detach().  

> 
> It means that an application that wants to use a private area has
> to provide another init function derived from this default function.

After your changes, attach/free and other functions from public mbuf API
rely on priv_size being set properly.
So I suppose 'official' pktmbuf_init() should also set it in a proper manner. 

> This was already the case before the patch series.

Before this patch series, we don't have priv_size, so we have nothing to setup.

> 
> As we discussed in previous mail, I plan to propose a rework of
> mbuf pool initialization in another series, and my initial idea was to
> change this at the same time. But on the other hand it does not hurt
> to do this change now. I'll include it in next version.

Ok.

> 
> 
> > BTW, don't see changes in rte_pktmbuf_pool_init() to setup
> > mbp_priv->mbuf_data_room_size properly.
> > Without that changes, how can people start using that feature?
> > It seems that the only way now - setup priv_size and buf_len for each mbuf manually.
> 
> It's the same reason than above. To use a private are, the user has
> to provide its own function that sets up data_room_size, derived from
> this pool_init default function. This was also the case before the
> patch series.
> 
> 
> >
> >>  }
> >>
> >>  /* do some sanity checks on a mbuf: panic if it fails */
> >> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> >> index 17ba791..932fe58 100644
> >> --- a/lib/librte_mbuf/rte_mbuf.h
> >> +++ b/lib/librte_mbuf/rte_mbuf.h
> >> @@ -317,18 +317,51 @@ struct rte_mbuf {
> >>  			/* uint64_t unused:8; */
> >>  		};
> >>  	};
> >> +
> >> +	/** Size of the application private data. In case of an indirect
> >> +	 * mbuf, it stores the direct mbuf private data size. */
> >> +	uint16_t priv_size;
> >>  } __rte_cache_aligned;
> >>
> >>  /**
> >> - * 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;
> >> +
> >> +       /* mi->buf_addr and mi->priv_size correspond to buffer and
> >> +	* private size of the direct mbuf */
> >> +       md = (struct rte_mbuf *)((char *)mi->buf_addr - sizeof(*mi) -
> >> +	       mi->priv_size);
> >
> > (uintptr_t)mi->buf_addr?
> 
> Any clue why (uintptr_t) would be better than (char *) ?

No big difference really, just looks a bit better to me :)

> By the way, I added this cast because it would not compile with
> g++ (and probably with icc too).
> 
> >
> >> +       return md;
> >> +}
> >>
> >>  /**
> >> - * 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.
> >> + *
> >> + * The user must ensure that m->priv_size corresponds to the
> >> + * private size of this mbuf, which is not the case for indirect
> >> + * mbufs.
> >> + *
> >> + * @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 *
> >
> > Might be better to return 'void *' here.
> 
> Ok, as m->buf_addr is a (void *).
> 
> >
> >> +rte_mbuf_to_baddr(struct rte_mbuf *md)
> >> +{
> >> +       char *buffer_addr;
> >
> > uintptr_t buffer_addr?
> 
> Same question than above, I don't really see why it's better than
> (char *).
> 
> >
> >> +       buffer_addr = (char *)md + sizeof(*md) + md->priv_size;
> >> +       return buffer_addr;
> >> +}
> >>
> >>  /**
> >>   * Returns TRUE if given mbuf is indirect, or FALSE otherwise.
> >> @@ -688,6 +721,7 @@ 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:
> >> @@ -701,7 +735,6 @@ 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) &&
> >> @@ -712,6 +745,7 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *md)
> >>  	mi->buf_physaddr = md->buf_physaddr;
> >>  	mi->buf_addr = md->buf_addr;
> >>  	mi->buf_len = md->buf_len;
> >> +	mi->priv_size = md->priv_size;
> >>
> >>  	mi->next = md->next;
> >>  	mi->data_off = md->data_off;
> >> @@ -732,7 +766,8 @@ 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.
> >> @@ -740,22 +775,28 @@ 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_pktmbuf_pool_private *mbp_priv;
> >> +	struct rte_mempool *mp = m->pool;
> >> +	void *buf;
> >> +	unsigned mhdr_size;
> >> +
> >> +	/* first, restore the priv_size, this is needed before calling
> >> +	 * rte_mbuf_to_baddr() */
> >> +	mbp_priv = rte_mempool_get_priv(mp);
> >> +	m->priv_size = mp->elt_size - RTE_PKTMBUF_HEADROOM -
> >> +		mbp_priv->mbuf_data_room_size -
> >> +		sizeof(struct rte_mbuf);
> >
> > I think it is better to put this priv_size calculation above into the separate function -
> > rte_mbuf_get_priv_size(m) or something.
> > We need it in few places, and users would probably need it anyway.
> 
> yep, good idea
> 
> >
> >> +
> >> +	buf = rte_mbuf_to_baddr(m);
> >> +	mhdr_size = (char *)buf - (char *)m;
> >
> > Why do you need to recalculate mhdr_size here?
> > As I understand it is a m->priv_size, and you just retrieved it, 2 lines above.
> >
> 
> It's not m->priv_size but (sizeof(rte_mbuf) + m->priv_size).

Ah yes, sorry for confusion.

> In both case, it requires an operation, but maybe
>   mhdr_size = (sizeof(rte_mbuf) + m->priv_size)
> is clearer than
>   mhdr_size = (char *)buf - (char *)m
> 
> 
> >> +	m->buf_physaddr = rte_mempool_virt2phy(mp, m) + mhdr_size;
> >
> > Actually I think could just be:
> > m->buf_physaddr = rte_mempool_virt2phy(mp, buf);
> 
> Even if it would work, the API of rte_mempool_virt2phy()
> says that the second argument should be "A pointer (virtual address)
> to the element of the pool."
> I think we should keep the initial code.

Ok.
Konstantin

> 
> Regards,
> Olivier
>