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

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

> -----Original Message-----
> From: Wiles, Keith
> Sent: Wednesday, March 20, 2019 5:53 PM
> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> Cc: dpdk-dev <dev@dpdk.org>; akhil.goyal@nxp.com; olivier.matz@6wind.com
> Subject: Re: [dpdk-dev] [PATCH v2 1/7] mbuf: new function to generate raw Tx offload value
> 
> 
> 
> > On Mar 20, 2019, at 10:24 AM, Konstantin Ananyev <konstantin.ananyev@intel.com> wrote:
> >
> > 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 naming of these fields is a bit unreadable and why do we need to add RTE_MBUF_ to everything especially adding RTE_ to everything.

It is part of public API, so I think we'll have to follow DPDK naming convention here.  

> Then we have to shorten words like OFFSET to OFS, it would be much better for readability to use something like this
> 
> RTE_MBUF_OL3_LEN_OFS to MBUF_OL3_LEN_OFFSET, then we have OL3 or OL2, which does not jump out at me as well.
> What does OL3 or OL2 mean? OffLoad-3 or OffLoad-2 this also needs to be clearly defined to improve the readability of the macros.

outer_l3_len, outer_l2_len.
These enum values follows tx_offload bit-fields definitions - see below.

> Also for TXOFLD needs to be clearer here to help the reader understand the mean of the defines.
> 
> 
> > +
> > /**
> >  * 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; */
> > 		};
> > 	};
> >
> > @@ -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
> >
> 
> Regards,
> Keith