Native VPP+DPDK plugin knows the size of rte_mbuf header and subtracts it
from the vlib pointer.
struct rte_mbuf *mb0 = rte_mbuf_from_vlib_buffer (b0);
#define rte_mbuf_from_vlib_buffer(x) (((struct rte_mbuf *)x) - 1)
On 7 December 2017 at 19:02, Bill Fischofer <bill.fischo...@linaro.org>
wrote:
> Ping to others on the mailing list for opinions on this. What does
> "native" VPP+DPDK get and how is this problem solved there?
>
> On Thu, Dec 7, 2017 at 11:55 AM, Michal Mazur <michal.ma...@linaro.org>
> wrote:
>
>> The _odp_packet_inline is common for all packets and takes up to two
>> cachelines (it contains only offsets). Reading pointer for each packet from
>> VLIB would require to fetch 10 million cachelines per second.
>> Using prefetches does not help.
>>
>> On 7 December 2017 at 18:37, Bill Fischofer <bill.fischo...@linaro.org>
>> wrote:
>>
>>> Yes, but _odp_packet_inline.udate is clearly not in the VLIB cache line
>>> either, so it's a separate cache line access. Are you seeing this
>>> difference in real runs or microbenchmarks? Why isn't the entire VLIB being
>>> prefetched at dispatch? Sequential prefetching should add negligible
>>> overhead.
>>>
>>> On Thu, Dec 7, 2017 at 11:13 AM, Michal Mazur <michal.ma...@linaro.org>
>>> wrote:
>>>
>>>> It seems that only first cache line of VLIB buffer is in L1, new
>>>> pointer can be placed only in second cacheline.
>>>> Using constant offset between user area and ODP header i get 11 Mpps,
>>>> with pointer stored in VLIB buffer only 10Mpps and with this new api
>>>> 10.6Mpps.
>>>>
>>>> On 7 December 2017 at 18:04, Bill Fischofer <bill.fischo...@linaro.org>
>>>> wrote:
>>>>
>>>>> How would calling an API be better than referencing the stored data
>>>>> yourself? A cache line reference is a cache line reference, and presumably
>>>>> the VLIB buffer is already in L1 since it's your active data.
>>>>>
>>>>> On Thu, Dec 7, 2017 at 10:45 AM, Michal Mazur <michal.ma...@linaro.org
>>>>> > wrote:
>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> For odp4vpp plugin we need a new API function which, given user area
>>>>>> pointer, will return a pointer to ODP packet buffer. It is needed when
>>>>>> packets processed by VPP are sent back to ODP and only a pointer to
>>>>>> VLIB
>>>>>> buffer data (stored inside user area) is known.
>>>>>>
>>>>>> I have tried to store the ODP buffer pointer in VLIB data but reading
>>>>>> it
>>>>>> for every packet lowers performance by 800kpps.
>>>>>>
>>>>>> For odp-dpdk implementation it can look like:
>>>>>> /** @internal Inline function @param uarea @return */
>>>>>> static inline odp_packet_t _odp_packet_from_user_area(void *uarea)
>>>>>> {
>>>>>> return (odp_packet_t)((uintptr_t)uarea -
>>>>>> _odp_packet_inline.udata);
>>>>>> }
>>>>>>
>>>>>> Please let me know what you think.
>>>>>>
>>>>>> Thanks,
>>>>>> Michal
>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>
>
