在 2023/12/4 15:41, Morten Brørup 写道:
From: Feifei Wang [mailto:feifei.wa...@arm.com]
Sent: Monday, 4 December 2023 03.39
For 'rte_pktmbuf_prefree_seg' function, 'rte_mbuf_refcnt_read(m) == 1'
and '__rte_mbuf_refcnt_update(m, -1) == 0' are the same cases where
mbuf's refcnt value should be 1. Thus we can simplify the code and
remove the redundant part.
Furthermore, according to [1], when the mbuf is stored inside the
mempool, the m->refcnt value should be 1. And then it is detached
from its parent for an indirect mbuf. Thus change the description of
'rte_pktmbuf_prefree_seg' function.
[1] https://patches.dpdk.org/project/dpdk/patch/20170404162807.20157-4-
olivier.m...@6wind.com/
Suggested-by: Ruifeng Wang <ruifeng.w...@arm.com>
Signed-off-by: Feifei Wang <feifei.wa...@arm.com>
---
lib/mbuf/rte_mbuf.h | 22 +++-------------------
1 file changed, 3 insertions(+), 19 deletions(-)
diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h
index 286b32b788..42e9b50d51 100644
--- a/lib/mbuf/rte_mbuf.h
+++ b/lib/mbuf/rte_mbuf.h
@@ -1328,7 +1328,7 @@ static inline int
__rte_pktmbuf_pinned_extbuf_decref(struct rte_mbuf *m)
*
* This function does the same than a free, except that it does not
* return the segment to its pool.
- * It decreases the reference counter, and if it reaches 0, it is
+ * It decreases the reference counter, and if it reaches 1, it is
No, the original description is correct.
However, the reference counter is set to 1 when put back in the pool, as a
shortcut so it isn't needed to be set back to 1 when allocated from the pool.
Ok.
for 'else if (__rte_mbuf_refcnt_update(m, -1) == 0)' case, it is easy to
understand.
but for '(likely(rte_mbuf_refcnt_read(m) == 1))' case, I think this will
create misleading. dpdk users maybe difficult to understand why the code
can not match the function description.
Maybe we need some explanation here?
* detached from its parent for an indirect mbuf.
*
* @param m
@@ -1358,25 +1358,9 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
The preceding "if (likely(rte_mbuf_refcnt_read(m) == 1)) {" is only a shortcut
for the likely case.
Ok.
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;
- rte_mbuf_refcnt_set(m, 1);
-
- return m;
}
+
+ __rte_mbuf_refcnt_update(m, -1);
return NULL;
}
--
2.25.1
NAK.
This patch is not race safe. With the patch:
This thread:
if (likely(rte_mbuf_refcnt_read(m) == 1)) { // Assume it's 2.
The other thread:
if (likely(rte_mbuf_refcnt_read(m) == 1)) { // It's 2.
__rte_mbuf_refcnt_update(m, -1); // Now it's 1.
return NULL;
This thread:
__rte_mbuf_refcnt_update(m, -1); // Now it's 0.
return NULL;
None of the threads have done the "prefree" work.
Agree. After we see the failture of unit_test, we realize that we
ignored the mutiple thread case.
Also maybe we need to add extra descripion to avoid misleading？
