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4ce78a838c
This patch speeds up the rx_poll function by reducing the number of
register reads.
Replace the 32bit register read by a 16bit register read. Currently
the 32bit register read is implemented by using 2 16bit reads. This is
inefficient as we only use the lower 16bit in rx_poll.
The for loop reads the pending interrupts in every iteration. This
leads up to 16 reads of pending interrupts. The patch introduces a new
outer loop to read the pending interrupts as long as 'quota' is above 0.
This reduces the total number of reads.
The third change is to replace the for-loop by a ffs loop.
Tested on AM335x. I removed all 'static' and 'inline' from c_can.c to
see the timings for all functions. I used the function tracer with
trace_stats.
125kbit:
Function Hit Time Avg s^2
-------- --- ---- --- ---
c_can_do_rx_poll 63960 10168178 us 158.977 us 1493056 us
With patch:
c_can_do_rx_poll 63941 3764057 us 58.867 us 776162.2 us
1Mbit:
Function Hit Time Avg s^2
-------- --- ---- --- ---
c_can_do_rx_poll 69489 30049498 us 432.435 us
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| .. | ||
| c_can_pci.c | ||
| c_can_platform.c | ||
| c_can.c | ||
| c_can.h | ||
| Kconfig | ||
| Makefile | ||