From: Stephen Hemminger <stephen@networkplumber.org>
To: Konstantin Ananyev <konstantin.ananyev@huawei.com>
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: Tue, 5 Dec 2023 10:50:32 -0800 [thread overview]
Message-ID: <20231205105032.4b81e3da@hermes.local> (raw)
In-Reply-To: <f86c58a6521142c6add96b8ff17bac65@huawei.com>
On Mon, 4 Dec 2023 11:07:08 +0000
Konstantin Ananyev <konstantin.ananyev@huawei.com> wrote:
> > > 2.25.1
> >
> > 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) ) {
+ /* 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;
+ }
- 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:[~2023-12-05 18:50 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 [this message]
2023-12-06 10:12 ` Bruce Richardson
2023-12-06 10:21 ` Konstantin Ananyev
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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