[dpdk-dev] [PATCH v2] mbuf: optimize rte_mbuf_refcnt_update
Olivier MATZ
olivier.matz at 6wind.com
Mon Jan 4 14:53:29 CET 2016
Hi Hanoch,
Please find some comments below.
On 12/27/2015 10:39 AM, Hanoch Haim (hhaim) wrote:
> Hi Bruce,
>
> I'm Hanoch from Cisco Systems works for the https://github.com/cisco-system-traffic-generator/trex-core traffic generator project.
>
> While upgrading from DPDK 1.8 to 2.2 Ido found that the following commit creates a mbuf corruption and result in Tx hang
>
>
>
> commit f20b50b946da9070d21e392e4dbc7d9f68bc983e
>
> Author: Olivier Matz <olivier.matz at 6wind.com>
>
> Date: Mon Jun 8 16:57:22 2015 +0200
>
>
>
> Looking at the change it is clear why there is an issue, wanted to get your input.
>
>
>
> Init
>
> -----
>
> alloc const mbuf ==> mbuf-a (ref=1)
>
>
>
> Simple case that works
>
> ---------------------
>
>
>
> thread 1 , tx: alloc-mbuf->attach(mbuf-a) (ref=2) inc- non atomic
>
> thread 1 , tx: alloc-mbuf->attach(mbuf-a) (ref32) inc- atomic
do you mean "(ref=3)" ?
>
> thread 1 , drv : free() (ref=2) dec- atomic
>
> thread 1 , drv : free() (ref=3) dec - non atomic
do you mean "(ref=1)" ?
>
> Simple case that does not work
>
> ---------------------
>
>
>
> Both do that in parallel
>
>
>
> thread 2 tx : alloc-mbuf->attach(mbuf-a) (ref=2) inc- non atomic
>
> thread 1 tx : alloc-mbuf->attach(mbuf-a) (ref=2) inc- non atomic
It is not allowed to call a function from the mbuf API in parallel.
Example:
core0 | core1
--------------------------------|---------------------------------------
m = rte_pktmbuf_alloc(m); |
enqueue(m); |
|m = dequeue();
do_something(m); |do_something(m);
do_something() is not allowed because it accesses the same mbuf
structure.
do_something() can be any function of mbuf API: rte_pktmbuf_prepend(),
rte_pktmbuf_attach(), ...
This is allowed:
core0 | core1
--------------------------------|---------------------------------------
m = rte_pktmbuf_alloc(m); |
m2 = rte_pktmbuf_attach(m); |
enqueue(m2); |
|m2 = dequeue();
do_something(m); |do_something(m2);
Regards,
Olivier
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