Re: [dpdk-dev] [PATCH v1 3/3] ethdev: enhance the API for getting burst mode information

["Wang, Haiyue" <haiyue.wang@intel.com>]

Hi Thomas,

Reply the missed:

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Saturday, November 2, 2019 06:46
> To: Wang, Haiyue <haiyue.wang@intel.com>
> Cc: dev@dpdk.org; arybchenko@solarflare.com; Yigit, Ferruh <ferruh.yigit@intel.com>;
> jerinjacobk@gmail.com; Ye, Xiaolong <xiaolong.ye@intel.com>; Kinsella, Ray <ray.kinsella@intel.com>;
> Sun, Chenmin <chenmin.sun@intel.com>; Slava Ovsiienko <viacheslavo@mellanox.com>
> Subject: Re: [PATCH v1 3/3] ethdev: enhance the API for getting burst mode information
> 
> Thank you for trying to address comments done late.
> 
> 31/10/2019 18:11, Haiyue Wang:
> > --- a/lib/librte_ethdev/rte_ethdev.h
> > +++ b/lib/librte_ethdev/rte_ethdev.h
> > -enum rte_eth_burst_mode_option {
> > -	RTE_ETH_BURST_SCALAR = (1 << 0),
> > -	RTE_ETH_BURST_VECTOR = (1 << 1),
> > -
> > -	/**< bits[15:2] are reserved for each vector type */
> > -	RTE_ETH_BURST_ALTIVEC = (1 << 2),
> > -	RTE_ETH_BURST_NEON = (1 << 3),
> > -	RTE_ETH_BURST_SSE = (1 << 4),
> > -	RTE_ETH_BURST_AVX2 = (1 << 5),
> > -	RTE_ETH_BURST_AVX512 = (1 << 6),
> > -
> > -	RTE_ETH_BURST_SCATTERED = (1 << 16), /**< Support scattered packets */
> > -	RTE_ETH_BURST_BULK_ALLOC = (1 << 17), /**< Support mbuf bulk alloc */
> > -	RTE_ETH_BURST_SIMPLE = (1 << 18),
> > -
> > -	RTE_ETH_BURST_PER_QUEUE = (1 << 19), /**< Support per queue burst */
> > -};
> > +#define RTE_ETH_BURST_SCALAR        (1ULL << 0)
> > +#define RTE_ETH_BURST_VECTOR        (1ULL << 1)
> 
> Only one bit is needed: if it is not vector, it is scalar.
> I think you can remove the scalar bit.
> 

1. 'options' can be all zero, so we can't assume it is 'scalar', so let's the PMD
    set it explicitly.

2. As replied before, it seems a little redundant, but a bit-opaque definition
   will make string format easily, like a direct 'for' loop:
   ----------------------------------
	static const struct {
		uint64_t option;
		const char *name;
	} rte_burst_option_names[] = {
		{ RTE_ETH_BURST_SCALAR, "Scalar" },
		{ RTE_ETH_BURST_VECTOR, "Vector" },

		{ RTE_ETH_BURST_ALTIVEC, "AltiVec" },
		{ RTE_ETH_BURST_NEON, "Neon" },
  ----------------------------------

And in fact, only one vector type will be returned, but if use the bit save definition
like register, there will be something like 'RTE_ETH_BURST_VERTOR_TYPE_MASK', this will
make PMD and string format harder ...


> > +/**< bits[15:2] are reserved for each vector type */
> 
> Why 15:2 instead of 2:15?
> 

Changed as:
/**< bits 2 ~ 15 are reserved for each vector type */

> > +#define RTE_ETH_BURST_ALTIVEC       (1ULL << 2)
> > +#define RTE_ETH_BURST_NEON          (1ULL << 3)
> > +#define RTE_ETH_BURST_SSE           (1ULL << 4)
> > +#define RTE_ETH_BURST_AVX2          (1ULL << 5)
> > +#define RTE_ETH_BURST_AVX512        (1ULL << 6)
> 
> Of course, I still believe that giving a special treatment
> to vector instructions is wrong.
> You did not justify why it needs to be defined in bits
> instead of string. I am not asking again because anyway you
> don't really reply. I think you are executing an order you received
> and I don't want to blame you more.
> I suspect a real hidden issue in Intel CPUs that you try to mitigate.
> No need to reply to this comment.
> Anyway I will propose to replace this API in the next release.
> 
> > +/**< Support per queue burst */
> > +#define RTE_ETH_BURST_PER_QUEUE     (1ULL << 63)
> 
> This comment is meaningless.
> If this bit has a usage, please explain how to use this bit
> in the comment.
> 

Changes as:

/**< If the Rx/Tx queues have different burst mode description, the bit will be
 * set by PMD, then the application can enumerate to retrive burst description
 * for all PMD queues.
 */