bvdberg opened a new issue, #1870:
URL: https://github.com/apache/mynewt-nimble/issues/1870
We are streaming data as fast as possible over BLE using the
ble_gatts_notify_custom call with a payload of 240 bytes.
Our connection interval is 6 (=7.5 ms), so around 133 Hz. Using a 2 Mbit
connection, we should be able to send at least 4 frames per interval (each
around 256 bytes including header). Right?
To get to around 1 Mbit/sec (payload, so 128 KB/sec), we need to send around
500 240 byte frames. So each frame can take 2 ms maximum. However, the
ble_gatts_notify_custom() takes 9 ms. Diving into this, it seems one call takes
up most time:
(call stack)
ble_gatts_notify_custom
ble_att_clt_tx_notify
ble_att_tx
ble_att_tx_with_conn
ble_l2cap_tx
ble_hs_hci_acl_tx
ble_hs_hci_acl_tx_now -> takes 8.9 ms in code fragment below
#if !BLE_MONITOR
BLE_HS_LOG(DEBUG, "ble_hs_hci_acl_tx(): ");
ble_hs_log_mbuf(frag);
BLE_HS_LOG(DEBUG, "\n");
#endif
We have disable the BLE_MONITOR, so the code fragment is active. The
ble_hs_log_mbuf seems to log byte per byte into a buffer, printed as hex.
Disabling this fragment speeds up the notify to 300 usec per call, so good
enough.
It seems weird to me that ble_hs_log is always called whenever BLE_MONITOR
is disabled. I would expect a separate HS_LOG define or something, that maybe
defines ble_hs_log_mbuf as nothing.
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