From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Monjalon <thomas.monjalon-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH] vhost: Check descriptor number for vector Rx
Date: Fri, 24 Oct 2014 11:27:31 +0200
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To: Ouyang Changchun <changchun.ouyang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
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Hi Changchun,

2014-10-24 16:38, Ouyang Changchun:
> For zero copy, it need check whether RX descriptor num meets the 
> least requirement when using vector PMD Rx function, and give user 
> more hints if it fails to meet the least requirement.
[...]
> --- a/examples/vhost/main.c
> +++ b/examples/vhost/main.c
> @@ -131,6 +131,10 @@
>  #define RTE_TEST_RX_DESC_DEFAULT_ZCP 32   /* legacy: 32, DPDK virt FE: 128. */
>  #define RTE_TEST_TX_DESC_DEFAULT_ZCP 64   /* legacy: 64, DPDK virt FE: 64.  */
>  
> +#ifdef RTE_IXGBE_INC_VECTOR
> +#define VPMD_RX_BURST         32
> +#endif
> +
>  /* Get first 4 bytes in mbuf headroom. */
>  #define MBUF_HEADROOM_UINT32(mbuf) (*(uint32_t *)((uint8_t *)(mbuf) \
>  		+ sizeof(struct rte_mbuf)))
> @@ -792,6 +796,19 @@ us_vhost_parse_args(int argc, char **argv)
>  		return -1;
>  	}
>  
> +#ifdef RTE_IXGBE_INC_VECTOR
> +	if ((zero_copy == 1) && (num_rx_descriptor <= VPMD_RX_BURST)) {
> +		RTE_LOG(INFO, VHOST_PORT,
> +			"The RX desc num: %d is too small for PMD to work\n"
> +			"properly, please enlarge it to bigger than %d if\n"
> +			"possible by the option: '--rx-desc-num <number>'\n"
> +			"One alternative is disabling RTE_IXGBE_INC_VECTOR\n"
> +			"in config file and rebuild the libraries.\n",
> +			num_rx_descriptor, VPMD_RX_BURST);
> +		return -1;
> +	}
> +#endif
> +
>  	return 0;
>  }

I feel there is a design problem here.
An application shouldn't have to care about the underlying driver.

-- 
Thomas