> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Stephen Hemminger
> Sent: Wednesday, December 23, 2015 6:38 PM
> To: Xie, Huawei
> Cc: dev at dpdk.org; dprovan at bivio.net
> Subject: Re: [dpdk-dev] [PATCH v3 1/2] mbuf: provide rte_pktmbuf_alloc_bulk
> API
>
> On Wed, 23 Dec 2015 00:17:53 +0800
> Huawei Xie <huawei.xie at intel.com> wrote:
>
> > +
> > + rc = rte_mempool_get_bulk(pool, (void **)mbufs, count);
> > + if (unlikely(rc))
> > + return rc;
> > +
> > + switch (count % 4) {
> > + case 0: while (idx != count) {
> > + 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;
> > +}
>
> Since function will not work if count can not be 0 (otherwise
> rte_mempool_get_bulk will fail),
As I understand, rte_mempool_get_bulk() will work correctly and return 0, if
count==0.
That's why Huawei prefers while() {}, instead of do {} while() - to avoid extra
check for
(count != 0) at the start.
Konstantin
> why not:
> 1. Document that assumption
> 2. Use that assumption to speed up code.
>
>
>
> switch(count % 4) {
> do {
> case 0:
> ...
> case 1:
> ...
> } while (idx != count);
> }
>
> Also you really need to add a big block comment about this loop, to explain
> what it does and why.
