[dpdk-dev] [PATCH] ring: guarantee ordering of cons/prod loading when doing enqueue/dequeue

[Jia He]

Hi Jerin


On 11/2/2017 4:57 PM, Jia He Wrote:
>
> Hi， Jerin
> please see my performance test below
> On 11/2/2017 3:04 AM, Jerin Jacob Wrote:
> [...]
>> Should it be like instead?
>>
>> +#else
>> +        *old_head = __atomic_load_n(&r->cons.head, __ATOMIC_ACQUIRE);
>> +        const uint32_t prod_tail = __atomic_load_n(&r->prod.tail,
>> __ATOMIC_ACQUIRE);
>> It would be nice to see how much overhead it gives.ie back to back
>> __ATOMIC_ACQUIRE.
> I can NOT test ring_perf_autotest in our server because of the 
> something wrong in PMU counter.
> All the return value of rte_rdtsc is 0 with and without your provided 
> ko module. I am still
> investigating the reason.
>

Hi Jerin

As for the root cause of rte_rdtsc issue, it might be due to the pmu 
counter frequency is too low

in our arm64 server("Amberwing" from qualcom)

[586990.057779] arch_timer_get_cntfrq()=20000000

Only 20MHz instead of 100M/200MHz, and CNTFRQ_EL0 is not even writable 
in kernel space.

Maybe the code in ring_perf_autotest needs to be changed?

e.g.

     printf("SC empty dequeue: %.2F\n",
             (double)(sc_end-sc_start) / iterations);
     printf("MC empty dequeue: %.2F\n",
             (double)(mc_end-mc_start) / iterations);

Otherwise it is always 0 if the time difference divides by iterations.


-- 
Cheers,
Jia