can: c_can: Speed up rx_poll function
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 9271851
us
With patch:
c_can_do_rx_poll 207109 24322185 us 117.436 us 171469047 us
Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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@ -808,17 +808,19 @@ static int c_can_do_rx_poll(struct net_device *dev, int quota)
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u32 num_rx_pkts = 0;
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unsigned int msg_obj, msg_ctrl_save;
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struct c_can_priv *priv = netdev_priv(dev);
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u32 val = c_can_read_reg32(priv, C_CAN_INTPND1_REG);
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u16 val;
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/*
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* It is faster to read only one 16bit register. This is only possible
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* for a maximum number of 16 objects.
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*/
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BUILD_BUG_ON_MSG(C_CAN_MSG_OBJ_RX_LAST > 16,
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"Implementation does not support more message objects than 16");
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while (quota > 0 && (val = priv->read_reg(priv, C_CAN_INTPND1_REG))) {
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while ((msg_obj = ffs(val)) && quota > 0) {
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val &= ~BIT(msg_obj - 1);
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for (msg_obj = C_CAN_MSG_OBJ_RX_FIRST;
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msg_obj <= C_CAN_MSG_OBJ_RX_LAST && quota > 0;
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val = c_can_read_reg32(priv, C_CAN_INTPND1_REG),
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msg_obj++) {
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/*
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* as interrupt pending register's bit n-1 corresponds to
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* message object n, we need to handle the same properly.
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*/
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if (val & (1 << (msg_obj - 1))) {
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c_can_object_get(dev, 0, msg_obj, IF_COMM_ALL &
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~IF_COMM_TXRQST);
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msg_ctrl_save = priv->read_reg(priv,
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