[dpdk-dev] [PATCH] ring: guarantee ordering of cons/prod loading when doing enqueue/dequeue

Zhao, Bing ilovethull at 163.com
Fri Oct 13 07:57:05 CEST 2017


Hi Jerin,

The patch is as below. Jie and I just modified from the original case.

 1. If all consumers(slave lcore) start to work after the producer fill
    the ring in every iteration test, there will be no problem.
 2. If only one consumer with one producer, there will not be any
    problem either.
 3. The more consumers are involved in, the higher reproduction rate
    will be observed.
 4. With the rmb, no issue is found in more than 100 thousands iteration
    tests.

./test/test/test -l 4-11 -n 6

test_refcnt_iter(lcore=4, iter=0) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=1) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=2) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=3) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=4) completed, 10 references processed
m ref is 2
test_refcnt_iter(lcore=4, iter=5) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=6) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=7) completed, 10 references processed
PANIC in __rte_ring_move_cons_head():
test_refcnt_iter(lcore=4, iter=8) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=9) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=10) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=11) completed, 10 references processed
m ref is 2
test_refcnt_iter(lcore=4, iter=12) completed, 10 references processed
m ref is 2
test_refcnt_iter(lcore=4, iter=13) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=14) completed, 10 references processed
test_refcnt_iter(lcore=4, iter=15) completed, 10 references processed
bizhao 4294967295 0x50 0x51 0x4f 0x50 0x50
m ref is 2

Note: only 0x50 of the filling operation and the PT is different in 
every read act (0x4f != 0x50), and CH > PT. It does not exceed the ring 
size(512) so the subtraction is overflow. Then since the CH is correct, 
so the CH with +1 is considered to be correct and over the PT.

Test Patch:

--------------------------------

diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
old mode 100644
new mode 100755
index 26a62b8..ba0a6db
--- a/lib/librte_mbuf/rte_mbuf.c
+++ b/lib/librte_mbuf/rte_mbuf.c
@@ -243,8 +243,8 @@ rte_pktmbuf_dump(FILE *f, const struct rte_mbuf *m, 
unsigned dump_len)

         __rte_mbuf_sanity_check(m, 1);

-       fprintf(f, "dump mbuf at %p, phys=%"PRIx64", buf_len=%u\n",
-              m, (uint64_t)m->buf_physaddr, (unsigned)m->buf_len);
+       fprintf(f, "dump mbuf at %p, phys=%"PRIx64", buf_len=%u, ref=%u\n",
+              m, (uint64_t)m->buf_physaddr, (unsigned)m->buf_len, 
(unsigned)m->refcnt);
         fprintf(f, "  pkt_len=%"PRIu32", ol_flags=%"PRIx64", nb_segs=%u, "
                "in_port=%u\n", m->pkt_len, m->ol_flags,
                (unsigned)m->nb_segs, (unsigned)m->port);
diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
old mode 100644
new mode 100755
index 8f5a493..3456b69
--- a/lib/librte_ring/rte_ring.h
+++ b/lib/librte_ring/rte_ring.h
@@ -502,6 +502,7 @@ __rte_ring_do_enqueue(struct rte_ring *r, void * 
const *obj_table,
   *   - Actual number of objects dequeued.
   *     If behavior == RTE_RING_QUEUE_FIXED, this will be 0 or n only.
   */
+#include <rte_debug.h>
  static __rte_always_inline unsigned int
  __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
                 unsigned int n, enum rte_ring_queue_behavior behavior,
@@ -517,6 +518,7 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
                 n = max;

                 *old_head = r->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
@@ -532,6 +534,8 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
                         return 0;

                 *new_head = *old_head + n;
+               if (*new_head > prod_tail) //|| r->cons.head > r->prod.tail)
+                       rte_panic("bizhao %u %#x %#x %#x %#x %#x\n", 
*entries, *old_head, *new_head, prod_tail, r->cons.head, r->prod.tail);
                 if (is_sc)
                         r->cons.head = *new_head, success = 1;
                 else
diff --git a/test/test/test_mbuf.c b/test/test/test_mbuf.c
old mode 100644
new mode 100755
index 3396b4a..731535c
--- a/test/test/test_mbuf.c
+++ b/test/test/test_mbuf.c
@@ -71,10 +71,12 @@
  /* size of private data for mbuf in pktmbuf_pool2 */
  #define MBUF2_PRIV_SIZE         128

-#define REFCNT_MAX_ITER         64
+// #define REFCNT_MAX_ITER         64
+#define REFCNT_MAX_ITER         32
  #define REFCNT_MAX_TIMEOUT      10
-#define REFCNT_MAX_REF          (RTE_MAX_LCORE)
-#define REFCNT_MBUF_NUM         64
+// #define REFCNT_MAX_REF          (RTE_MAX_LCORE)
+#define REFCNT_MAX_REF          512
+#define REFCNT_MBUF_NUM         1
  #define REFCNT_RING_SIZE        (REFCNT_MBUF_NUM * REFCNT_MAX_REF)

  #define MAGIC_DATA              0x42424242
@@ -683,12 +685,18 @@ test_refcnt_slave(void *arg)

         lcore = rte_lcore_id();
         printf("%s started at lcore %u\n", __func__, lcore);
+       uint32_t ava;

         free = 0;
         while (refcnt_stop_slaves == 0) {
-               if (rte_ring_dequeue(refcnt_mbuf_ring, &mp) == 0) {
+               ava = rte_ring_dequeue_bulk(refcnt_mbuf_ring, &mp ,1, NULL);
+               if (ava > 0) {
+                       if (ava > 10) {
+                               rte_panic("OMG %u %u\n", 
refcnt_mbuf_ring->prod.tail, refcnt_mbuf_ring->cons.tail);
+                       }
                         free++;
-                       rte_pktmbuf_free(mp);
+                       // rte_pktmbuf_free(mp);
+                       rte_pktmbuf_refcnt_update(mp, -1);
                 }
         }

@@ -719,6 +727,7 @@ test_refcnt_iter(unsigned int lcore, unsigned int iter,
             i != n && (m = rte_pktmbuf_alloc(refcnt_pool)) != NULL;
             i++) {
                 ref = RTE_MAX(rte_rand() % REFCNT_MAX_REF, 1UL);
+               ref = 10;
                 tref += ref;
                 if ((ref & 1) != 0) {
                         rte_pktmbuf_refcnt_update(m, ref);
@@ -730,7 +739,7 @@ test_refcnt_iter(unsigned int lcore, unsigned int iter,
rte_ring_enqueue(refcnt_mbuf_ring, m);
                         }
                 }
-               rte_pktmbuf_free(m);
+               // rte_pktmbuf_free(m);
         }

         if (i != n)
@@ -741,6 +750,12 @@ test_refcnt_iter(unsigned int lcore, unsigned int iter,
         while (!rte_ring_empty(refcnt_mbuf_ring))
                 ;

+       if (NULL != m) {
+               if (1 != rte_mbuf_refcnt_read(m))
+                       printf("m ref is %u\n", rte_mbuf_refcnt_read(m));
+               rte_pktmbuf_free(m);
+       }
+
         /* check that all mbufs are back into mempool by now */
         for (wn = 0; wn != REFCNT_MAX_TIMEOUT; wn++) {
                 if ((i = rte_mempool_avail_count(refcnt_pool)) == n) {
(END)

--------------------------------

BR. Bing

On 2017/10/13 11:23, Jia He wrote:
> Hi Jerin
>
>
> On 10/13/2017 9:49 AM, Jerin Jacob Wrote:
>> -----Original Message-----
>>> Date: Fri, 13 Oct 2017 09:16:31 +0800
>>> From: Jia He <hejianet at gmail.com>
>>> To: Jerin Jacob <jerin.jacob at caviumnetworks.com>, "Ananyev, Konstantin"
>>>   <konstantin.ananyev at intel.com>
>>> Cc: Olivier MATZ <olivier.matz at 6wind.com>, "dev at dpdk.org" 
>>> <dev at dpdk.org>,
>>>   "jia.he at hxt-semitech.com" <jia.he at hxt-semitech.com>,
>>>   "jie2.liu at hxt-semitech.com" <jie2.liu at hxt-semitech.com>,
>>>   "bing.zhao at hxt-semitech.com" <bing.zhao at hxt-semitech.com>
>>> Subject: Re: [PATCH] ring: guarantee ordering of cons/prod loading when
>>>   doing enqueue/dequeue
>>> User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
>>>   Thunderbird/52.3.0
>>>
>>> Hi
>>>
>>>
>>> On 10/13/2017 9:02 AM, Jia He Wrote:
>>>> Hi Jerin
>>>>
>>>>
>>>> On 10/13/2017 1:23 AM, Jerin Jacob Wrote:
>>>>> -----Original Message-----
>>>>>> Date: Thu, 12 Oct 2017 17:05:50 +0000
>>>>>>
>>> [...]
>>>>> On the same lines,
>>>>>
>>>>> Jia He, jie2.liu, bing.zhao,
>>>>>
>>>>> Is this patch based on code review or do you saw this issue on any
>>>>> of the
>>>>> arm/ppc target? arm64 will have performance impact with this change.
>>> sorry, miss one important information
>>> Our platform is an aarch64 server with 46 cpus.
>> Is this an OOO(Out of order execution) aarch64 CPU implementation?
> I think so, it is a server cpu (ARMv8-A), but do you know how to 
> confirm it?
> cat /proc/cpuinfo
> processor       : 0
> BogoMIPS        : 40.00
> Features        : fp asimd evtstrm aes pmull sha1 sha2 crc32 cpuid 
> asimdrdm
> CPU implementer : 0x51
> CPU architecture: 8
> CPU variant     : 0x0
> CPU part        : 0x800
> CPU revision    : 0
>>> If we reduced the involved cpu numbers, the bug occurred less 
>>> frequently.
>>>
>>> Yes, mb barrier impact the performance, but correctness is more 
>>> important,
>>> isn't it ;-)
>> Yes.
>>
>>> Maybe we can  find any other lightweight barrier here?
>> Yes, Regarding the lightweight barrier, arm64 has native support for 
>> acquire and release
>> semantics, which is exposed through gcc as architecture agnostic
>> functions.
>> https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html
>> http://preshing.com/20130922/acquire-and-release-fences/
>>
>> Good to know,
>> 1) How much overhead this patch in your platform? Just relative
>> numbers are enough
> I create a *standalone* test case for test_mbuf
> Attached the debug patch
> It is hard to believe but the truth is that the performance after 
> adding rmb barrier
> is better than no adding.
>
> With this patch (4 times running)
> time ./test_good --no-huge -l 1-20
> real    0m23.311s
> user    7m21.870s
> sys     0m0.021s
>
> time ./test_bad --no-huge -l 1-20
> Without this patch
> real    0m38.972s
> user    12m35.271s
> sys     0m0.030s
>
> Cheers,
> Jia
>> 2) As a prototype, Is Changing to acquire and release schematics
>> reduces the overhead in your platform?
>>
>> Reference FreeBSD ring/DPDK style ring implementation through acquire
>> and release schematics
>> https://github.com/Linaro/odp/blob/master/platform/linux-generic/pktio/ring.c 
>>
>>
>> I will also spend on cycles on this.
>>
>>
>>> Cheers,
>>> Jia
>>>> Based on mbuf_autotest, the rte_panic will be invoked in seconds.
>>>>
>>>> PANIC in test_refcnt_iter():
>>>> (lcore=0, iter=0): after 10s only 61 of 64 mbufs left free
>>>> 1: [./test(rte_dump_stack+0x38) [0x58d868]]
>>>> Aborted (core dumped)
>>>>
>>>> Cheers,
>>>> Jia
>>>>>
>>>>>> Konstantin
>



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