From: Linzhe Lee <slayercat.subscription@gmail.com>
To: Stephen Hemminger <stephen@networkplumber.org>, dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] mbuf: fix atomic refcnt update synchronization
Date: Sat, 3 Sep 2016 00:31:50 +0800 [thread overview]
Message-ID: <CAK_yBkNMQHNG-bLci08HHiOSfcy5zAau6m19KJaVtBYNU_xhMg@mail.gmail.com> (raw)
In-Reply-To: <20160902091236.57250d1a@xeon-e3>
Thanks for reply, Stephen.
I'm in x86-64, my cpu is `Intel(R) Xeon(R) CPU E5-2620 v3 @ 2.40GHz`.
When allocation mbuf in program1, and transfer it to program2 for free
via ring, the program1 might meet assert in allocate mbuf sometimes.
(`RTE_ASSERT(rte_mbuf_refcnt_read(m) == 0);`)
but when I using gdb to check it, the refcnt field of mbuf is already
zero. so I believe the problem came from the cache line problem or
incorrect optimization.
When apply this patch, the problem seems solved. I'm submitting it for
your comments.
2016-09-03 0:12 GMT+08:00 Stephen Hemminger <stephen@networkplumber.org>:
> On Fri, 2 Sep 2016 13:25:06 +0800
> lilinzhe <slayercat.subscription@gmail.com> wrote:
>
>> From: 李林哲 <lilinzhe@ijinshan.com>
>>
>> chagne atomic ref update to always call atomic_add
>>
>> when mbuf is allocated by cpu1 and freed by cpu2. cpu1 cache may not be updated by such a set operation.
>> causes refcnt reads incorrect values.
>
> What architecture are you dealing with? On X86 memory is cache coherent.
>
> Doing atomic operation all the time on each mbuf free would significantly
> slow down performance.
>
next prev parent reply other threads:[~2016-09-02 16:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-02 5:25 lilinzhe
2016-09-02 16:12 ` Stephen Hemminger
2016-09-02 16:31 ` Linzhe Lee [this message]
2016-09-02 16:51 ` Stephen Hemminger
2016-09-03 2:05 ` Linzhe Lee
2016-09-03 22:52 ` Ananyev, Konstantin
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