[dpdk-dev] [PATCH 2/2] Adding the routines rte_pktmbuf_alloc_bulk() and rte_pktmbuf_free_bulk()

Wiles, Roger Keith keith.wiles at windriver.com
Mon Oct 6 21:45:27 CEST 2014


On Oct 6, 2014, at 11:13 AM, Wiles, Roger Keith <keith.wiles at windriver.com> wrote:

>
> On Oct 6, 2014, at 10:54 AM, Ananyev, Konstantin <konstantin.ananyev at intel.com> wrote:
>
>>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Bruce Richardson
>>> Sent: Monday, October 06, 2014 3:54 PM
>>> To: Wiles, Roger Keith (Wind River)
>>> Cc: dev at dpdk.org
>>> Subject: Re: [dpdk-dev] [PATCH 2/2] Adding the routines rte_pktmbuf_alloc_bulk() and rte_pktmbuf_free_bulk()
>>>
>>> On Mon, Oct 06, 2014 at 03:50:38PM +0100, Wiles, Roger Keith wrote:
>>>> Hi Bruce,
>>>>
>>>> Do I need to reject the for the new routines or just make sure the vector driver does not get updated to use those routines?
>>>>
>>>
>>> The new routines are probably useful in the general case. I see no issue
>>> with having them in the code, so long as the vector driver is not modified
>>> to use them.
>>
>> I 'd say the same thing for non-vector RX/TX PMD code-paths too.
>>
>> BTW, are the new functions comments valid?
>>
>> + * @return
>> + *   - 0 if the number of mbufs allocated was ok
>> + *   - <0 is an ERROR.
>> + */
>> +static inline int __rte_mbuf_raw_alloc_bulk(
>>
>> Though, as I can see __rte_mbuf_raw_alloc_bulk() returns either:
>> - number of  allocated mbuf (cnt)
>> - negative error code
>
> Let me fix up the comments.
>>
>> And:
>> + * @return
>> + *   - The number of valid mbufs pointers in the m_list array.
>> + *   - Zero if the request cnt could not be allocated.
>> + */
>> +static inline int __attribute__((always_inline))
>> +rte_pktmbuf_alloc_bulk(struct rte_mempool *mp, struct rte_mbuf *m_list[], int16_t cnt)
>> +{
>> +     return __rte_mbuf_raw_alloc_bulk(mp, m_list, cnt);
>> +}
>>
>> Shouldn't be "less than zero if the request cnt could not be allocated."?
>>
>> BTW, is there any point to have __rte_mbuf_raw_alloc_bulk() at all?
>> After all, as you are calling rte_pktmbuf_reset() inside it, it doesn't look __raw__ any more.
>> Might be just put its content into rte_pktmbuf_alloc_bulk() and get rid of it.
>>
> I was just following the non-bulk routine style __rte_mbuf_raw_alloc(), but I can pull that into a single routine.
>
>> Also wonder, what is the advantage of having multiple counters inside the same loop?
>> i.e:
>> +             for(i = 0; i < cnt; i++) {
>> +                     m = *m_list++;
>>
>> Why not just:
>>
>> for(i = 0; i < cnt; i++) {
>>   m = &m_list[i];
>>
>> Same for free:
>> +     while(npkts--)
>> +             rte_pktmbuf_free(*m_list++);
>>
>> While not just:
>> for (i = 0; i < npkts; i++)
>>     rte_pktmbuf_free(&m_list[i]);
>
> Maybe I have it wrong or the compilers are doing the right thing now, but at one point the &m_list[i] would cause the compiler to generate a shift or multiple of ‘i’ and then add it to the base of m_list. If that is not the case anymore then I can update the code as you suggested. Using the *m_list++ just adds the size of a pointer to a register and continues.

I compared the clang assembler (.s file) output from an example test code I wrote to see if we have any differences in the code using the two styles and I found no difference and the code looked the same. I am not a Intel assembler expert and I would suggest someone else determine if it generates different code. I tried to compare the GCC outputs and it did look the same to me.

I have attached the code and output, please let me know if I did something wrong, but as it stands using the original style is what I want to go with.

>>
>> Konstantin
>>
>>>
>>> /Bruce
>>>
>>>> Thanks
>>>> ++Keith
>>>>
>>>> On Oct 6, 2014, at 3:56 AM, Richardson, Bruce <bruce.richardson at intel.com> wrote:
>>>>
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Keith Wiles
>>>>>> Sent: Sunday, October 05, 2014 12:10 AM
>>>>>> To: dev at dpdk.org
>>>>>> Subject: [dpdk-dev] [PATCH 2/2] Adding the routines rte_pktmbuf_alloc_bulk()
>>>>>> and rte_pktmbuf_free_bulk()
>>>>>>
>>>>>> Minor helper routines to mirror the mempool routines and remove the code
>>>>>> from applications. The ixgbe_rxtx_vec.c routine could be changed to use
>>>>>> the ret_pktmbuf_alloc_bulk() routine inplace of rte_mempool_get_bulk().
>>>>>>
>>>>>
>>>>> I believe such a change would cause a performance regression, as the extra init code in the alloc_bulk() function would take
>>> additional cycles and is not needed. The vector routines use the mempool function directly, so that there is no overhead of mbuf
>>> initialization, as the vector routines use their additional "knowledge" of what the mbufs will be used for to init them in a faster manner
>>> than can be done inside the mbuf library.
>>>>>
>>>>> /Bruce
>>>>>
>>>>>> Signed-off-by: Keith Wiles <keith.wiles at windriver.com>
>>>>>> ---
>>>>>> lib/librte_mbuf/rte_mbuf.h | 77
>>>>>> ++++++++++++++++++++++++++++++++++++++++++++++
>>>>>> 1 file changed, 77 insertions(+)
>>>>>>
>>>>>> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
>>>>>> index 1c6e115..f298621 100644
>>>>>> --- a/lib/librte_mbuf/rte_mbuf.h
>>>>>> +++ b/lib/librte_mbuf/rte_mbuf.h
>>>>>> @@ -546,6 +546,41 @@ static inline void rte_pktmbuf_reset(struct rte_mbuf
>>>>>> *m)
>>>>>> }
>>>>>>
>>>>>> /**
>>>>>> + * @internal Allocate a list of mbufs from mempool *mp*.
>>>>>> + * The use of that function is reserved for RTE internal needs.
>>>>>> + * Please use rte_pktmbuf_alloc_bulk().
>>>>>> + *
>>>>>> + * @param mp
>>>>>> + *   The mempool from which mbuf is allocated.
>>>>>> + * @param m_list
>>>>>> + *   The array to place the allocated rte_mbufs pointers.
>>>>>> + * @param cnt
>>>>>> + *   The number of mbufs to allocate
>>>>>> + * @return
>>>>>> + *   - 0 if the number of mbufs allocated was ok
>>>>>> + *   - <0 is an ERROR.
>>>>>> + */
>>>>>> +static inline int __rte_mbuf_raw_alloc_bulk(struct rte_mempool *mp, struct
>>>>>> rte_mbuf *m_list[], int cnt)
>>>>>> +{
>>>>>> +     struct rte_mbuf *m;
>>>>>> +     int             ret;
>>>>>> +
>>>>>> +     ret = rte_mempool_get_bulk(mp, (void **)m_list, cnt);
>>>>>> +     if ( ret == 0 ) {
>>>>>> +             int             i;
>>>>>> +             for(i = 0; i < cnt; i++) {
>>>>>> +                     m = *m_list++;
>>>>>> +#ifdef RTE_MBUF_REFCNT
>>>>>> +                     rte_mbuf_refcnt_set(m, 1);
>>>>>> +#endif /* RTE_MBUF_REFCNT */
>>>>>> +                     rte_pktmbuf_reset(m);
>>>>>> +             }
>>>>>> +             ret = cnt;
>>>>>> +     }
>>>>>> +     return ret;
>>>>>> +}
>>>>>> +
>>>>>> +/**
>>>>>> * Allocate a new mbuf from a mempool.
>>>>>> *
>>>>>> * This new mbuf contains one segment, which has a length of 0. The pointer
>>>>>> @@ -671,6 +706,32 @@ __rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>>>>>> }
>>>>>>
>>>>>> /**
>>>>>> + * Allocate a list of mbufs from a mempool into a mbufs array.
>>>>>> + *
>>>>>> + * This mbuf list contains one segment per mbuf, which has a length of 0. The
>>>>>> pointer
>>>>>> + * to data is initialized to have some bytes of headroom in the buffer
>>>>>> + * (if buffer size allows).
>>>>>> + *
>>>>>> + * The routine is just a simple wrapper routine to reduce code in the application
>>>>>> and
>>>>>> + * provide a cleaner API for multiple mbuf requests.
>>>>>> + *
>>>>>> + * @param mp
>>>>>> + *   The mempool from which the mbuf is allocated.
>>>>>> + * @param m_list
>>>>>> + *   An array of mbuf pointers, cnt must be less then or equal to the size of the
>>>>>> list.
>>>>>> + * @param cnt
>>>>>> + *   Number of slots in the m_list array to fill.
>>>>>> + * @return
>>>>>> + *   - The number of valid mbufs pointers in the m_list array.
>>>>>> + *   - Zero if the request cnt could not be allocated.
>>>>>> + */
>>>>>> +static inline int __attribute__((always_inline))
>>>>>> +rte_pktmbuf_alloc_bulk(struct rte_mempool *mp, struct rte_mbuf *m_list[],
>>>>>> int16_t cnt)
>>>>>> +{
>>>>>> +     return __rte_mbuf_raw_alloc_bulk(mp, m_list, cnt);
>>>>>> +}
>>>>>> +
>>>>>> +/**
>>>>>> * Free a segment of a packet mbuf into its original mempool.
>>>>>> *
>>>>>> * Free an mbuf, without parsing other segments in case of chained
>>>>>> @@ -708,6 +769,22 @@ static inline void rte_pktmbuf_free(struct rte_mbuf
>>>>>> *m)
>>>>>>    }
>>>>>> }
>>>>>>
>>>>>> +/**
>>>>>> + * Free a list of packet mbufs back into its original mempool.
>>>>>> + *
>>>>>> + * Free a list of mbufs by calling rte_pktmbuf_free() in a loop as a wrapper
>>>>>> function.
>>>>>> + *
>>>>>> + * @param m_list
>>>>>> + *   An array of rte_mbuf pointers to be freed.
>>>>>> + * @param npkts
>>>>>> + *   Number of packets to free in list.
>>>>>> + */
>>>>>> +static inline void rte_pktmbuf_free_bulk(struct rte_mbuf *m_list[], int16_t
>>>>>> npkts)
>>>>>> +{
>>>>>> +     while(npkts--)
>>>>>> +             rte_pktmbuf_free(*m_list++);
>>>>>> +}
>>>>>> +
>>>>>> #ifdef RTE_MBUF_REFCNT
>>>>>>
>>>>>> /**
>>>>>> --
>>>>>> 2.1.0
>>>>>
>>>>
>>>> Keith Wiles, Principal Technologist with CTO office, Wind River mobile 972-213-5533
>
> Keith Wiles, Principal Technologist with CTO office, Wind River mobile 972-213-5533

Keith Wiles, Principal Technologist with CTO office, Wind River mobile 972-213-5533



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