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
>>>>>
>>>>
>>>>
>>>
>>
>
