From: Jia He <hejianet@gmail.com>
To: olivier.matz@6wind.com
Cc: dev@dpdk.org, Jia He <hejianet@gmail.com>,
jia.he@hxt-semitech.com, jie2.liu@hxt-semitech.com,
bing.zhao@hxt-semitech.com
Subject: [dpdk-dev] [PATCH] ring: guarantee ordering of cons/prod loading when doing enqueue/dequeue
Date: Tue, 10 Oct 2017 17:56:36 +0800 [thread overview]
Message-ID: <20171010095636.4507-1-hejianet@gmail.com> (raw)
Before this patch:
In __rte_ring_move_cons_head()
...
do {
/* Restore n as it may change every loop */
n = max;
*old_head = r->cons.head; //1st load
const uint32_t prod_tail = r->prod.tail; //2nd load
In weak memory order architectures(powerpc,arm), the 2nd load might be
reodered before the 1st load, that makes *entries is bigger than we wanted.
This nasty reording messed enque/deque up.
cpu1(producer) cpu2(consumer) cpu3(consumer)
load r->prod.tail
in enqueue:
load r->cons.tail
load r->prod.head
store r->prod.tail
load r->cons.head
load r->prod.tail
...
store r->cons.{head,tail}
load r->cons.head
THEN,r->cons.head will be bigger than prod_tail, then make *entries very big
After this patch, the old cons.head will be recaculated after failure of
rte_atomic32_cmpset
There is no such issue in X86 cpu, because X86 is strong memory order model
Signed-off-by: Jia He <hejianet@gmail.com>
Signed-off-by: jia.he@hxt-semitech.com
Signed-off-by: jie2.liu@hxt-semitech.com
Signed-off-by: bing.zhao@hxt-semitech.com
---
lib/librte_ring/rte_ring.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
index 5e9b3b7..15c72e2 100644
--- a/lib/librte_ring/rte_ring.h
+++ b/lib/librte_ring/rte_ring.h
@@ -409,6 +409,10 @@ __rte_ring_move_prod_head(struct rte_ring *r, int is_sp,
n = max;
*old_head = r->prod.head;
+
+ /* load of prod.tail can't be reordered before cons.head */
+ rte_smp_rmb();
+
const uint32_t cons_tail = r->cons.tail;
/*
* The subtraction is done between two unsigned 32bits value
@@ -517,6 +521,10 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
n = max;
*old_head = r->cons.head;
+
+ /* load of prod.tail can't be reordered before cons.head */
+ rte_smp_rmb();
+
const uint32_t prod_tail = r->prod.tail;
/* The subtraction is done between two unsigned 32bits value
* (the result is always modulo 32 bits even if we have
--
2.7.4
next reply other threads:[~2017-10-10 9:56 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-10 9:56 Jia He [this message]
2017-10-12 15:53 ` Olivier MATZ
2017-10-12 16:15 ` Stephen Hemminger
2017-10-12 17:05 ` Ananyev, Konstantin
2017-10-12 17:23 ` Jerin Jacob
2017-10-13 1:02 ` Jia He
2017-10-13 1:15 ` Jia He
2017-10-13 1:16 ` Jia He
2017-10-13 1:49 ` Jerin Jacob
2017-10-13 3:23 ` Jia He
2017-10-13 5:57 ` Zhao, Bing
2017-10-13 7:33 ` Jianbo Liu
2017-10-13 8:20 ` Jia He
2017-10-19 10:02 ` Ananyev, Konstantin
2017-10-19 11:18 ` Zhao, Bing
2017-10-19 14:15 ` Ananyev, Konstantin
2017-10-19 20:02 ` Ananyev, Konstantin
2017-10-20 1:57 ` Jia He
2017-10-20 5:43 ` Jerin Jacob
2017-10-23 8:49 ` Jia He
2017-10-23 9:05 ` Kuusisaari, Juhamatti
2017-10-23 9:10 ` Bruce Richardson
2017-10-23 10:06 ` Jerin Jacob
2017-10-24 2:04 ` Jia He
2017-10-25 13:26 ` Jerin Jacob
2017-10-26 2:27 ` Jia He
2017-10-31 2:55 ` Jia He
2017-10-31 11:14 ` Jerin Jacob
2017-11-01 2:53 ` Jia He
2017-11-01 19:04 ` Jerin Jacob
2017-11-02 1:09 ` Jia He
2017-11-02 8:57 ` Jia He
2017-11-03 2:55 ` Jia He
2017-11-03 12:47 ` Jerin Jacob
2017-11-01 4:48 ` Jia He
2017-11-01 19:10 ` Jerin Jacob
2017-10-20 7:03 ` Ananyev, Konstantin
2017-10-13 0:24 ` Liu, Jie2
2017-10-13 2:12 ` Zhao, Bing
2017-10-13 2:34 ` Jerin Jacob
2017-10-16 10:51 ` Kuusisaari, Juhamatti
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