From: Konstantin Ananyev <konstantin.ananyev@huawei.com>
To: Bruce Richardson <bruce.richardson@intel.com>,
Stephen Hemminger <stephen@networkplumber.org>
Cc: "Morten Brørup" <mb@smartsharesystems.com>,
"Feifei Wang" <feifei.wang2@arm.com>,
"dev@dpdk.org" <dev@dpdk.org>, "nd@arm.com" <nd@arm.com>,
"Ruifeng Wang" <ruifeng.wang@arm.com>
Subject: RE: [PATCH v1] mbuf: remove the redundant code for mbuf prefree
Date: Wed, 6 Dec 2023 10:21:29 +0000 [thread overview]
Message-ID: <a6e7bfc0745848ddbab8f51c8b4e5984@huawei.com> (raw)
In-Reply-To: <ZXBI9ZGggeHC2Z_9@bricha3-MOBL.ger.corp.intel.com>
> > > >
> > > > NAK.
> > > >
> > > > This patch is not race safe.
> > >
> > > +1, It is a bad idea.
> >
> > The patch does raise a couple of issues that could be addressed by
> > rearranging. There is duplicate code, and there are no comments
> > to explain the rationale.
> >
> > Maybe something like the following (untested):
> >
> > diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h
> > index 286b32b788a5..b43c055fbe3f 100644
> > --- a/lib/mbuf/rte_mbuf.h
> > +++ b/lib/mbuf/rte_mbuf.h
> > @@ -1342,42 +1342,32 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > {
> > __rte_mbuf_sanity_check(m, 0);
> >
> > - if (likely(rte_mbuf_refcnt_read(m) == 1)) {
> > -
> > - if (!RTE_MBUF_DIRECT(m)) {
> > - rte_pktmbuf_detach(m);
> > - if (RTE_MBUF_HAS_EXTBUF(m) &&
> > - RTE_MBUF_HAS_PINNED_EXTBUF(m) &&
> > - __rte_pktmbuf_pinned_extbuf_decref(m))
> > - return NULL;
> > - }
> > -
> > - if (m->next != NULL)
> > - m->next = NULL;
> > - if (m->nb_segs != 1)
> > - m->nb_segs = 1;
> > -
> > - return m;
> > -
> > - } else if (__rte_mbuf_refcnt_update(m, -1) == 0) {
> > -
> > - if (!RTE_MBUF_DIRECT(m)) {
> > - rte_pktmbuf_detach(m);
> > - if (RTE_MBUF_HAS_EXTBUF(m) &&
> > - RTE_MBUF_HAS_PINNED_EXTBUF(m) &&
> > - __rte_pktmbuf_pinned_extbuf_decref(m))
> > - return NULL;
> > - }
> > -
> > - if (m->next != NULL)
> > - m->next = NULL;
> > - if (m->nb_segs != 1)
> > - m->nb_segs = 1;
> > + if (likely(rte_mbuf_refcnt_read(m) != 1) ) {
>
> == 1
>
> > + /* If this is the only reference to the mbuf it can just
> > + * be setup for reuse without modifying reference count.
> > + */
> > + } else if (unlikely(__rte_mbuf_refcnt_update(m, -1) == 0)) {
> > + /* This was last reference reset to 1 for recycling/free. */
> > rte_mbuf_refcnt_set(m, 1);
> > + } else {
> > + /* mbuf is still in use */
> > + return NULL;
> > + }
> >
>
> This seems much clearer with good comments.
Then, it could be just:
/* put whatever likely/unlikely we believe would be the most common case */
if (rte_mbuf_refcnt_read(m) != 1 && __rte_mbuf_refcnt_update(m, -1) != 0)
return NULL;
/* do whatever cleanup is necessary */
>
> > - return m;
> > + if (!RTE_MBUF_DIRECT(m)) {
> > + rte_pktmbuf_detach(m);
> > + if (RTE_MBUF_HAS_EXTBUF(m) &&
> > + RTE_MBUF_HAS_PINNED_EXTBUF(m) &&
> > + __rte_pktmbuf_pinned_extbuf_decref(m))
> > +
> > + return NULL;
> > }
> > - return NULL;
> > +
> > + if (m->next != NULL)
> > + m->next = NULL;
> > + if (m->nb_segs != 1)
> > + m->nb_segs = 1;
> > + return m;
> > }
> >
> > /**
next prev parent reply other threads:[~2023-12-06 10:21 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-04 2:39 Feifei Wang
2023-12-04 7:41 ` Morten Brørup
2023-12-04 11:07 ` Konstantin Ananyev
2023-12-05 18:50 ` Stephen Hemminger
2023-12-06 10:12 ` Bruce Richardson
2023-12-06 10:21 ` Konstantin Ananyev [this message]
2023-12-05 3:13 ` Feifei Wang
2023-12-05 8:04 ` Morten Brørup
2023-12-05 9:53 ` Bruce Richardson
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