Re: [PATCH v3 2/2] mempool: pktmbuf pool default fallback for mempool ops error

[Hemant Agrawal <hemant.agrawal@nxp.com>]

Hi Olivier,
	Any updates w.r.t this patch set?

Regards
Hemant
On 9/22/2016 6:42 PM, Hemant Agrawal wrote:
> Hi Olivier
>
> On 9/19/2016 7:27 PM, Olivier Matz wrote:
>> Hi Hemant,
>>
>> On 09/16/2016 06:46 PM, Hemant Agrawal wrote:
>>> In the rte_pktmbuf_pool_create, if the default external mempool is
>>> not available, the implementation can default to "ring_mp_mc", which
>>> is an software implementation.
>>>
>>> Signed-off-by: Hemant Agrawal <hemant.agrawal@nxp.com>
>>> ---
>>> Changes in V3:
>>> * adding warning message to say that falling back to default sw pool
>>> ---
>>>  lib/librte_mbuf/rte_mbuf.c | 8 ++++++++
>>>  1 file changed, 8 insertions(+)
>>>
>>> diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
>>> index 4846b89..8ab0eb1 100644
>>> --- a/lib/librte_mbuf/rte_mbuf.c
>>> +++ b/lib/librte_mbuf/rte_mbuf.c
>>> @@ -176,6 +176,14 @@ rte_pktmbuf_pool_create(const char *name,
>>> unsigned n,
>>>
>>>      rte_errno = rte_mempool_set_ops_byname(mp,
>>>              RTE_MBUF_DEFAULT_MEMPOOL_OPS, NULL);
>>> +
>>> +    /* on error, try falling back to the software based default pool */
>>> +    if (rte_errno == -EOPNOTSUPP) {
>>> +        RTE_LOG(WARNING, MBUF, "Default HW Mempool not supported. "
>>> +            "falling back to sw mempool \"ring_mp_mc\"");
>>> +        rte_errno = rte_mempool_set_ops_byname(mp, "ring_mp_mc", NULL);
>>> +    }
>>> +
>>>      if (rte_errno != 0) {
>>>          RTE_LOG(ERR, MBUF, "error setting mempool handler\n");
>>>          return NULL;
>>>
>>
>> Without adding a new method ".supported()", the first call to
>> rte_mempool_populate() could return the same error ENOTSUP. In this
>> case, it is still possible to fallback.
>>
> It will be bit late.
>
> On failure, than we have to set the default ops and do a goto before
> rte_pktmbuf_pool_init(mp, &mbp_priv);
>
>
>> I've just submitted an RFC, which I think is quite linked:
>> http://dpdk.org/ml/archives/dev/2016-September/046974.html
>> Assuming a new parameter "mempool_ops" is added to
>> rte_pktmbuf_pool_create(), would it make sense to fallback to
>> "ring_mp_mc"? What about just returning ENOTSUP? The application could
>> do the job and decide which sw fallback to use.
>
> We ran into this issue when trying to run the standard DPDK examples
> (l3fwd) in VM. Do you think, is it practical to add fallback handling in
> each of the DPDK examples?
>
> Typically when someone is writing a application on host, he need not
> worry non-availability of the hw offloaded mempool. He may also want to
> run the same binary in virtual machine. In VM, it is not guaranteed that
> hw offloaded mempools will be available.
>
> w.r.t your RFC, we can do this:
> if the user has specified a mempool_ops in rte_pktmbuf_pool_create(),
> don't fallback. It will be responsibility for application to decide on
> calling again rte_pktmbuf_pool_create() with different mempool_ops.
>
>>
>>
>> Regards,
>> Olivier
>>
>
>
>