Re: [dpdk-dev] [PATCH v2 1/7] mbuf: new function to generate raw Tx offload value

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

Hi Shahaf,

> Hi Konstantin,
> 
> Wednesday, March 20, 2019 8:47 PM, Konstantin Ananyev:
> > Subject: [dpdk-dev] [PATCH v2 1/7] mbuf: new function to generate raw Tx
> > offload value
> >
> > Operations to set/update bit-fields often cause compilers to generate
> > suboptimal code.
> > To help avoid such situation for tx_offload fields:
> > introduce new enum for tx_offload bit-fields lengths and offsets, and new
> > function to generate raw tx_offload value.
> >
> > Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> > ---
> >  lib/librte_mbuf/rte_mbuf.h | 71
> > ++++++++++++++++++++++++++++++++++----
> >  1 file changed, 64 insertions(+), 7 deletions(-)
> >
> > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h index
> > d961ccaf6..b967ad17e 100644
> > --- a/lib/librte_mbuf/rte_mbuf.h
> > +++ b/lib/librte_mbuf/rte_mbuf.h
> > @@ -479,6 +479,26 @@ struct rte_mbuf_sched {
> >  	uint16_t reserved;   /**< Reserved. */
> >  }; /**< Hierarchical scheduler */
> >
> > +/** enum for the tx_offload bit-fields lenghts and offsets. */ enum {
> > +	RTE_MBUF_L2_LEN_BITS = 7,
> > +	RTE_MBUF_L3_LEN_BITS = 9,
> > +	RTE_MBUF_L4_LEN_BITS = 8,
> > +	RTE_MBUF_TSO_SEGSZ_BITS = 16,
> > +	RTE_MBUF_OL3_LEN_BITS = 9,
> > +	RTE_MBUF_OL2_LEN_BITS = 7,
> > +	RTE_MBUF_L2_LEN_OFS = 0,
> > +	RTE_MBUF_L3_LEN_OFS = RTE_MBUF_L2_LEN_OFS +
> > RTE_MBUF_L2_LEN_BITS,
> > +	RTE_MBUF_L4_LEN_OFS = RTE_MBUF_L3_LEN_OFS +
> > RTE_MBUF_L3_LEN_BITS,
> > +	RTE_MBUF_TSO_SEGSZ_OFS = RTE_MBUF_L4_LEN_OFS +
> > RTE_MBUF_L4_LEN_BITS,
> > +	RTE_MBUF_OL3_LEN_OFS = RTE_MBUF_TSO_SEGSZ_OFS +
> > RTE_MBUF_TSO_SEGSZ_BITS,
> > +	RTE_MBUF_OL2_LEN_OFS = RTE_MBUF_OL3_LEN_OFS +
> > RTE_MBUF_OL3_LEN_BITS,
> > +	RTE_MBUF_TXOFLD_UNUSED_OFS =
> > +		RTE_MBUF_OL2_LEN_OFS + RTE_MBUF_OL2_LEN_BITS,
> > +	RTE_MBUF_TXOFLD_UNUSED_BITS =
> > +		sizeof(uint64_t) * CHAR_BIT -
> > RTE_MBUF_TXOFLD_UNUSED_OFS, };
> > +
> >  /**
> >   * The generic rte_mbuf, containing a packet mbuf.
> >   */
> > @@ -640,19 +660,24 @@ struct rte_mbuf {
> >  		uint64_t tx_offload;       /**< combined for easy fetch */
> >  		__extension__
> >  		struct {
> > -			uint64_t l2_len:7;
> > +			uint64_t l2_len:RTE_MBUF_L2_LEN_BITS;
> >  			/**< L2 (MAC) Header Length for non-tunneling pkt.
> >  			 * Outer_L4_len + ... + Inner_L2_len for tunneling
> > pkt.
> >  			 */
> > -			uint64_t l3_len:9; /**< L3 (IP) Header Length. */
> > -			uint64_t l4_len:8; /**< L4 (TCP/UDP) Header Length.
> > */
> > -			uint64_t tso_segsz:16; /**< TCP TSO segment size */
> > +			uint64_t l3_len:RTE_MBUF_L3_LEN_BITS;
> > +			/**< L3 (IP) Header Length. */
> > +			uint64_t l4_len:RTE_MBUF_L4_LEN_BITS;
> > +			/**< L4 (TCP/UDP) Header Length. */
> > +			uint64_t tso_segsz:RTE_MBUF_TSO_SEGSZ_BITS;
> > +			/**< TCP TSO segment size */
> >
> >  			/* fields for TX offloading of tunnels */
> > -			uint64_t outer_l3_len:9; /**< Outer L3 (IP) Hdr
> > Length. */
> > -			uint64_t outer_l2_len:7; /**< Outer L2 (MAC) Hdr
> > Length. */
> > +			uint64_t outer_l3_len:RTE_MBUF_OL3_LEN_BITS;
> > +			/**< Outer L3 (IP) Hdr Length. */
> > +			uint64_t outer_l2_len:RTE_MBUF_OL2_LEN_BITS;
> > +			/**< Outer L2 (MAC) Hdr Length. */
> >
> > -			/* uint64_t unused:8; */
> > +			/* uint64_t
> > unused:RTE_MBUF_TXOFLD_UNUSED_BITS; */
> 
> I am not sure we want to decide now that this remaining byte is for another Tx offloads.

Not sure, I understand what is your concern here...
tx_offload field is 8B long, see 'uint64_t tx_offload' above.
All I did replaced raw number '8' with enum value ' RTE_MBUF_TXOFLD_UNUSED_BITS' which also evalueate to 8.

> Maybe it is better to change a bit the rte_mbuf_tx_offload API to receive also the mbuf and to assign the offload values w/ mask.

Could you explain a bit more what do you suggest here?
Konstantin


> 
> >  		};
> >  	};
> >
> > @@ -2243,6 +2268,38 @@ static inline int rte_pktmbuf_chain(struct
> > rte_mbuf *head, struct rte_mbuf *tail
> >  	return 0;
> >  }
> >
> > +/*
> > + * @warning
> > + * @b EXPERIMENTAL: This API may change without prior notice.
> > + *
> > + * For given input values generate raw tx_offload value.
> > + * @param il2
> > + *   l2_len value.
> > + * @param il3
> > + *   l3_len value.
> > + * @param il4
> > + *   l4_len value.
> > + * @param tso
> > + *   tso_segsz value.
> > + * @param ol3
> > + *   outer_l3_len value.
> > + * @param ol2
> > + *   outer_l2_len value.
> > + * @return
> > + *   raw tx_offload value.
> > + */
> > +static inline uint64_t
> > +rte_mbuf_tx_offload(uint64_t il2, uint64_t il3, uint64_t il4, uint64_t tso,
> > +	uint64_t ol3, uint64_t ol2)
> > +{
> > +	return il2 << RTE_MBUF_L2_LEN_OFS |
> > +		il3 << RTE_MBUF_L3_LEN_OFS |
> > +		il4 << RTE_MBUF_L4_LEN_OFS |
> > +		tso << RTE_MBUF_TSO_SEGSZ_OFS |
> > +		ol3 << RTE_MBUF_OL3_LEN_OFS |
> > +		ol2 << RTE_MBUF_OL2_LEN_OFS;
> > +}
> > +
> >  /**
> >   * Validate general requirements for Tx offload in mbuf.
> >   *
> > --
> > 2.17.1