BLE subsystem host RAM increase when migrating from NCS 2.5.0 to 2.7.0

[PuffinEgg]

Hi,

I am hit with a noticeable ram usage bump (~10%) when migrating from 2.5.0 to 2.7.0. Upon generating the ram_report, I notice that net_buf_data_hci_rx_pool has a huge ram usage increase (from 1.5k to 5k) while all of the BT configs remain to be the same. Therefore, I would like to know if there is anyway for me to reduce this amount. Thanks!

[Susheel Nuguru]

I have checked the peripheral_uart sample and net_buf_data_hci_rx_pool changed from 730->740 bytes in this sample.

Looking into the host\buf.c it looks like this buffer is depending on 

CONFIG_BT_BUF_EVT_RX_COUNT
CONFIG_BT_BUF_EVT_RX_SIZE
CONFIG_BT_BUF_ACL_RX_COUNT 
CONFIG_BT_BUF_ACL_RX_SIZE

Check if these things changed in your new port. I do not see anything else affecting this.

[PuffinEgg]

For some reason BT_BUF_EVT_RX_COUNT was set to 10, and BT_BUF_ACL_RX_COUNT was set to 6. Both of them were set to 3 in the previous SDK version(2.5.0). I manually changed them back to 3 and I was able to get back to the memory usage before. However, I am not sure which module is setting these numbers and I am a bit concerned to if I should manually set them to a lower value.

[PuffinEgg]

Actually, I see the default was 3 when  COFIG_BT_RECV_IS_RX_THREAD is selected. However, the default seems to be set to 10 and 6 for the latest version, and COFIG_BT_RECV_IS_RX_THREAD no longer seem to exist?