[dpdk-dev] [PATCH dpdk-dev v3] mempool: sort the rte_mempool_ops by name

[Tonghao Zhang]

On Tue, Mar 24, 2020 at 5:36 PM Andrew Rybchenko
<arybchenko at solarflare.com> wrote:
>
> On 3/9/20 11:27 AM, Olivier Matz wrote:
> > Hi,
> >
> > On Mon, Mar 09, 2020 at 11:01:25AM +0800, Tonghao Zhang wrote:
> >> On Sat, Mar 7, 2020 at 8:54 PM Andrew Rybchenko
> >> <arybchenko at solarflare.com> wrote:
> >>>
> >>> On 3/7/20 3:51 PM, Andrew Rybchenko wrote:
> >>>> On 3/6/20 4:37 PM, Jerin Jacob wrote:
> >>>>> On Fri, Mar 6, 2020 at 7:06 PM <xiangxia.m.yue at gmail.com> wrote:
> >>>>>> From: Tonghao Zhang <xiangxia.m.yue at gmail.com>
> >>>>>>
> >>>>>> The order of mempool initiation affects mempool index in the
> >>>>>> rte_mempool_ops_table. For example, when building APPs with:
> >>>>>>
> >>>>>> $ gcc -lrte_mempool_bucket -lrte_mempool_ring ...
> >>>>>>
> >>>>>> The "bucket" mempool will be registered firstly, and its index
> >>>>>> in table is 0 while the index of "ring" mempool is 1. DPDK
> >>>>>> uses the mk/rte.app.mk to build APPs, and others, for example,
> >>>>>> Open vSwitch, use the libdpdk.a or libdpdk.so to build it.
> >>>>>> The mempool lib linked in dpdk and Open vSwitch is different.
> >>>>>>
> >>>>>> The mempool can be used between primary and secondary process,
> >>>>>> such as dpdk-pdump and pdump-pmd/Open vSwitch(pdump enabled).
> >>>>>> There will be a crash because dpdk-pdump creates the "ring_mp_mc"
> >>>>>> ring which index in table is 0, but the index of "bucket" ring
> >>>>>> is 0 in Open vSwitch. If Open vSwitch use the index 0 to get
> >>>>>> mempool ops and malloc memory from mempool. The crash will occur:
> >>>>>>
> >>>>>>      bucket_dequeue (access null and crash)
> >>>>>>      rte_mempool_get_ops (should get "ring_mp_mc",
> >>>>>>                           but get "bucket" mempool)
> >>>>>>      rte_mempool_ops_dequeue_bulk
> >>>>>>      ...
> >>>>>>      rte_pktmbuf_alloc
> >>>>>>      rte_pktmbuf_copy
> >>>>>>      pdump_copy
> >>>>>>      pdump_rx
> >>>>>>      rte_eth_rx_burst
> >>>>>>
> >>>>>> To avoid the crash, there are some solution:
> >>>>>> * constructor priority: Different mempool uses different
> >>>>>>    priority in RTE_INIT, but it's not easy to maintain.
> >>>>>>
> >>>>>> * change mk/rte.app.mk: Change the order in mk/rte.app.mk to
> >>>>>>    be same as libdpdk.a/libdpdk.so, but when adding a new mempool
> >>>>>>    driver in future, we must make sure the order.
> >>>>>>
> >>>>>> * register mempool orderly: Sort the mempool when registering,
> >>>>>>    so the lib linked will not affect the index in mempool table.
> >>>>>>
> >>>>>> Signed-off-by: Tonghao Zhang <xiangxia.m.yue at gmail.com>
> >>>>>> Acked-by: Olivier Matz <olivier.matz at 6wind.com>
> >>>>> Acked-by: Jerin Jacob <jerinj at marvell.com>
> >>>>
> >>>> The patch is OK, but the fact that ops index changes during
> >>>> mempool driver lifetime is frightening. In fact it breaks
> >>>> rte_mempool_register_ops() return value semantics (read
> >>>> as API break). The return value is not used in DPDK, but it
> >>>> is a public function. If I'm not mistaken it should be taken
> >>>> into account.
> >
> > Good points.
> >
> > The fact that the ops index changes during mempool driver lifetime is
> > indeed frightening, especially knowning that this is a dynamic
> > registration that could happen at any moment in the life of the
> > application. Also, breaking the ABI is not desirable.
> >
> > Let me try to propose something else to solve your issue:
> >
> > 1/ At init, the primary process allocates a struct in shared memory
> >    (named memzone):
> >
> >    struct rte_mempool_shared_ops {
> >      size_t num_mempool_ops;
> >      struct {
> >        char name[RTE_MEMPOOL_OPS_NAMESIZE];
> >      } mempool_ops[RTE_MEMPOOL_MAX_OPS_IDX];
> >      char *mempool_ops_name[RTE_MEMPOOL_MAX_OPS_IDX];
> >      rte_spinlock_t mempool;
> >    }
> >
> > 2/ When we register a mempool ops, we first get a name and id from the
> >    shared struct: with the lock held, lookup for the registered name and
> >    return its index, else get the last id and copy the name in the struct.
> >
> > 3/ Then do as before (in the per-process global table), except that we
> >    reuse the registered id.
> >
> > We can remove the num_ops field from rte_mempool_ops_table.
> >
> > Thoughts?
>
> I like the solution.
The patch will be sent, thanks.


-- 
Best regards, Tonghao