Re: [PATCH v2] ixgbe: fix check for split packets

[Zoltan Kiss <zoltan.kiss@linaro.org>]

On 22/07/15 10:59, Bruce Richardson wrote:
> On Wed, Jul 22, 2015 at 10:47:34AM +0100, Zoltan Kiss wrote:
>> Hi,
>>
>> And what happens if someone changes RTE_IXGBE_VPMD_RX_BURST to something
>> else than 32? I guess this bug were introduced when someone raised it from
>> 16 to 32
>
> Actually, no, this bug is purely due to me getting my maths wrong when I
> wrote this function. The vector PMD has always worked in bursts of 32 at a
> time.
>
>> I think you are better off with a for loop which uses this value. Or at
>> least make a comment around RTE_IXGBE_VPMD_RX_BURST that if you change that
>> value this check should be modified as well.
>
> The vector PMD always works off a fixed 32 burst size. Any change to that will
> lead to many changes in the code, so I don't believe a loop is necessary.

Ok, then I suggest to make a comment around RTE_IXGBE_VPMD_RX_BURST that 
changing it needs a lot of other changes in the code elsewhere, e.g in 
this split_flags check.
Btw. vPMD was a bit misleading abbreviation for me, it took me a while 
until I realized 'v' stands for 'vector', not 'virtualization' as in 
most cases nowadays.

>
> Regards,
> /Bruce
>
>>
>> Regards,
>>
>> Zoltan
>>
>> On 22/07/15 10:13, Bruce Richardson wrote:
>>> The check for split packets to be reassembled in the vector ixgbe PMD
>>> was incorrectly only checking the first 16 elements of the array instead
>>> of all 32. This is fixed by changing the uint32_t values to be uint64_t
>>> instead.
>>>
>>> Fixes: cf4b4708a88a ("ixgbe: improve slow-path perf with vector scattered Rx")
>>>
>>> Reported-by: Zoltan Kiss <zoltan.kiss@linaro.org>
>>> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
>>>
>>> ---
>>> V2: Rename variable from split_fl32 to split_fl64 to match type change.
>>> ---
>>>   drivers/net/ixgbe/ixgbe_rxtx_vec.c | 6 +++---
>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>> index d3ac74a..f2052c6 100644
>>> --- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>> +++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>> @@ -549,10 +549,10 @@ ixgbe_recv_scattered_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
>>>   		return 0;
>>>
>>>   	/* happy day case, full burst + no packets to be joined */
>>> -	const uint32_t *split_fl32 = (uint32_t *)split_flags;
>>> +	const uint64_t *split_fl64 = (uint64_t *)split_flags;
>>>   	if (rxq->pkt_first_seg == NULL &&
>>> -			split_fl32[0] == 0 && split_fl32[1] == 0 &&
>>> -			split_fl32[2] == 0 && split_fl32[3] == 0)
>>> +			split_fl64[0] == 0 && split_fl64[1] == 0 &&
>>> +			split_fl64[2] == 0 && split_fl64[3] == 0)
>>>   		return nb_bufs;
>>>
>>>   	/* reassemble any packets that need reassembly*/
>>>