Re: [dpdk-dev] [PATCH v2 0/5] maximize vector rx burst for PMDs

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

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Saturday, August 29, 2020 04:31
> To: Guo, Jia <jia.guo@intel.com>
> Cc: Wang, Haiyue <haiyue.wang@intel.com>; Morten Brørup <mb@smartsharesystems.com>; Yang, Qiming
> <qiming.yang@intel.com>; Xing, Beilei <beilei.xing@intel.com>; Zhao1, Wei <wei.zhao1@intel.com>; Zhang,
> Qi Z <qi.z.zhang@intel.com>; Wu, Jingjing <jingjing.wu@intel.com>; Richardson, Bruce
> <bruce.richardson@intel.com>; dev@dpdk.org; Zhang, Helin <helin.zhang@intel.com>; Yigit, Ferruh
> <ferruh.yigit@intel.com>; barbette@kth.se
> Subject: Re: [dpdk-dev] [PATCH v2 0/5] maximize vector rx burst for PMDs
> 
> On Fri, 28 Aug 2020 14:39:33 +0800
> Jeff Guo <jia.guo@intel.com> wrote:
> 
> > >> I am not sure about this, but if I read it correctly, calling rte_eth_rx_burst() with nb_pkts =
> 33
> > >> (not 32) would only return 32 packets, even if more packets are available. (I assume that
> > >> RTE_I40E_DESCS_PER_LOOP is 32.) In this case, I guess that you need to read the remaining of the
> > >> requested packets using the non-vector function in order to support any nb_pkts value.
> > >>
> > > This is vector instruction handling design requirement, like for avx2: #define
> ICE_DESCS_PER_LOOP_AVX 8,
> > > if deep into the real loop handling, you will get the point why doing RTE_ALIGN_FLOOR. ;-)
> > >
> > > _ice_recv_raw_pkts_vec_avx2:
> > > for (i = 0, received = 0; i < nb_pkts; i += ICE_DESCS_PER_LOOP_AVX, rxdp += ICE_DESCS_PER_LOOP_AVX)
> > >
> > > Maybe it is worth to tell PMD to stop using vector by calling rte_eth_rx_queue_setup with the
> application
> > > burst size it wants.
> 
> There is no need for yet another nerd knob in DPDK.
> 
> The driver must accept any burst size > 0.
> If it wants to optimize for certain multiples, then it can do so in its burst handler.
> Like any optimized checksum calculator does.

I think if people care about performance, then PMDs have done every possible methods like
the burst size, then no need to invent their burst handers. ;-)

At least, burst size is an optimize hit for performance.