Allocating more RX descriptors that can fit in their related rings

[Karthikeyan Periyasamy]

corrected the statement below

On 9/6/2024 9:27 AM, Karthikeyan Periyasamy wrote:
> 
> 
> On 9/4/2024 11:31 PM, Remi Pommarel wrote:
>> Hello,
>>
>> As far as I understand a bunch (ATH12K_RX_DESC_COUNT) of rx descriptors
>> gets allocated, then CMEM is configured for those descriptors cookie
>> conversion and is kept available in dp->rx_desc_free_list pool.
>>
>> Those descriptors seem to be used to fed two different rings, the
>> rx_refill_buf_ring ring via ath12k_dp_rx_bufs_replenish() and the
>> reo_reinject_ring one with ath12k_dp_rx_h_defrag_reo_reinject(). While
>> the former is kept fully used if possible the latter is only used on
>> demand (i.e. reinjection of defragmented MPDU).
>>
>> It seems that the number of RX descriptors ATH12K_RX_DESC_COUNT (12288)
>> is higher than what those two rings can fit (DP_REO_REINJECT_RING_SIZE +
>> DP_RXDMA_BUF_RING_SIZE = 4096 + 32 = 4128).
>>
>> My question is why are we allocating that much (12288) buffer if only a
>> small part (4128) can be used in worst case ?
>> > Wouldn't it be ok to only allocate just enough RX descriptors to fill
>> both ring (with proper 512 alignment to ease CMEM configuration) as
>> below ?
>>
>>   #define ATH12K_RX_DESC_COUNT   ALIGN(DP_REO_REINJECT_RING_SIZE + \
>>                                        DP_RXDMA_BUF_RING_SIZE, \
>>                                        ATH12K_MAX_SPT_ENTRIES)
>>
>> Or am I missing something and this is going to impact performances ?
>>
> 
> Yes, it will impact performance.
> 
> Host replenish RxDMA buffers to the HW and after processing it given 
> back to Rx path (REO, WBM Error, Rx Error). So it can be relate to 
> one-to-one direct mapping. HW consume in-progress Rx buffer depend on 
> Data rate mode. If RxDMA buffers not available then it impact 
> performance due to Out-of-order Rx error due to RxDMA buffer unavailable.
> 

Yes, it will impact performance.

Host replenish RxDMA buffers to the HW and after processing it given
back to Rx path (REO, WBM Error, Rx Error). So it cannot be relate to
one-to-one direct mapping. HW consume in-progress Rx buffer depend on
Data rate mode. If RxDMA buffers not available then it impact
performance due to Out-of-order Rx error due to RxDMA buffer unavailable.

-- 
Karthikeyan Periyasamy
--
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