On 07/07/2024 18:18, Mihai Brodschi wrote:
>
>
> On 07/07/2024 17:05, Ferruh Yigit wrote:
>>
>> My expectation is numbers should be like following:
>>
>> Initially:
>> size = 256
>> head = 0
>> tail = 0
>>
>> In first refill:
>> n_slots = 256
>> head = 256
>> tail = 0
>>
>> Subsequent run that 32 slots used:
>> head = 256
>> tail = 32
>> n_slots = 32
>> rte_pktmbuf_alloc_bulk(mq, buf[head & mask], n_slots);
>> head & mask = 0
>> // So it fills first 32 elements of buffer, which is inbound
>>
>> This will continue as above, combination of only gap filled and head
>> masked with 'mask' provides the wrapping required.
>
> If I understand correctly, this works only if eth_memif_rx_zc always processes
> a number of packets which is a power of 2, so that the ring's head always
> wraps
> around at the end of a refill loop, never in the middle of it.
> Is there any reason this should be the case?
> Maybe the tests don't trigger the crash because this condition holds true for
> them?
Here's how to reproduce the crash on DPDK stable 23.11.1, using testpmd:
Server:
# ./dpdk-testpmd --vdev=net_memif0,id=1,role=server,bsize=1024,rsize=8
--single-file-segments -l2,3 --file-prefix test1 -- -i
Client:
# ./dpdk-testpmd
--vdev=net_memif0,id=1,role=client,bsize=1024,rsize=8,zero-copy=yes
--single-file-segments -l4,5 --file-prefix test2 -- -i
testpmd> start
Server:
testpmd> start tx_first
testpmt> set burst 15
At this point, the client crashes with a segmentation fault.
Before the burst is set to 15, its default value is 32.
If the receiver processes packets in bursts of size 2^N, the crash does not
occur.
Setting the burst size to any power of 2 works, anything else crashes.
After applying this patch, the crashes are completely gone.
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