On 12/22/2015 5:32 AM, Thomas Monjalon wrote: > 2015-12-21 17:20, Wiles, Keith: >> On 12/21/15, 9:21 AM, "Xie, Huawei" <huawei.xie at intel.com> wrote: >>> On 12/19/2015 3:27 AM, Wiles, Keith wrote: >>>> On 12/18/15, 11:32 AM, "dev on behalf of Stephen Hemminger" <dev-bounces >>>> at dpdk.org on behalf of stephen at networkplumber.org> wrote: >>>>> On Fri, 18 Dec 2015 10:44:02 +0000 >>>>> "Ananyev, Konstantin" <konstantin.ananyev at intel.com> wrote: >>>>>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Stephen Hemminger >>>>>>> On Mon, 14 Dec 2015 09:14:41 +0800 >>>>>>> Huawei Xie <huawei.xie at intel.com> wrote: >>>>>>>> + switch (count % 4) { >>>>>>>> + while (idx != count) { >>>>>>>> + case 0: >>>>>>>> + >>>>>>>> RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0); >>>>>>>> + rte_mbuf_refcnt_set(mbufs[idx], 1); >>>>>>>> + rte_pktmbuf_reset(mbufs[idx]); >>>>>>>> + idx++; >>>>>>>> + case 3: >>>>>>>> + >>>>>>>> RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0); >>>>>>>> + rte_mbuf_refcnt_set(mbufs[idx], 1); >>>>>>>> + rte_pktmbuf_reset(mbufs[idx]); >>>>>>>> + idx++; >>>>>>>> + case 2: >>>>>>>> + >>>>>>>> RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0); >>>>>>>> + rte_mbuf_refcnt_set(mbufs[idx], 1); >>>>>>>> + rte_pktmbuf_reset(mbufs[idx]); >>>>>>>> + idx++; >>>>>>>> + case 1: >>>>>>>> + >>>>>>>> RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0); >>>>>>>> + rte_mbuf_refcnt_set(mbufs[idx], 1); >>>>>>>> + rte_pktmbuf_reset(mbufs[idx]); >>>>>>>> + idx++; >>>>>>>> + } >>>>>>>> + } >>>>>>>> + return 0; >>>>>>>> +} >>>>>>> This is weird. Why not just use Duff's device in a more normal manner. >>>>>> But it is a sort of Duff's method. >>>>>> Not sure what looks weird to you here? >>>>>> while () {} instead of do {} while();? >>>>>> Konstantin >>>>>> >>>>>> >>>>>> >>>>> It is unusual to have cases not associated with block of the switch. >>>>> Unusual to me means, "not used commonly in most code". >>>>> >>>>> Since you are jumping into the loop, might make more sense as a do { } >>>>> while() >>>> I find this a very odd coding practice and I would suggest we not do this, >>>> unless it gives us some great performance gain. >>>> >>>> Keith >>> The loop unwinding could give performance gain. The only problem is the >>> switch/loop combination makes people feel weird at the first glance but >>> soon they will grasp this style. Since this is inherited from old famous >>> duff's device, i prefer to keep this style which saves lines of code. >> Please add a comment to the code to reflex where this style came from and >> why you are using it, would be very handy here. > +1 > At least the words "loop" and "unwinding" may be helpful to some readers. OK. Will add more context. Probably the wiki page for duff's device should be updated on how to handle the case count is zero, using while() or add one line to check.
> Thanks >
