Tracing shows k_busy_wait() being executed very often on nRF platforms

[carlescufi]

As per the screenshots below, provided by @nashif, k_busy_wait() is executing repeatedly on traces obtained on a Nordic board.

This can be reproduced by building samples/synchronization with tracing enabled.

nRF Platform:

k64f Platform:

[nordic-krch]

It is expected. k_busy_wait(1) is used inside uart_poll_out when driver is pending for driver readiness to send next byte. Safe loop is used there which is using k_busy_wait to track timeout.

zephyr/drivers/serial/uart_nrfx_uarte.c

Line 483 in 5e9d6d6

NRFX_WAIT_FOR(is_tx_ready(dev), 100, 1, res);