diff options
| author | Markus Pargmann <mpa@pengutronix.de> | 2013-11-01 13:36:36 +0400 |
|---|---|---|
| committer | Marc Kleine-Budde <mkl@pengutronix.de> | 2013-12-17 14:47:19 +0400 |
| commit | 4ce78a838c1c5482aeb47cfba9baf9df90400a25 (patch) | |
| tree | 5885bec1033265b6134bad75b53c7dc12c183f5e /drivers/net/can | |
| parent | 89e47d3b8a273b0eac21e4bf6d7fdb86b654fa16 (diff) | |
| download | linux-4ce78a838c1c5482aeb47cfba9baf9df90400a25.tar.xz | |
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>
Diffstat (limited to 'drivers/net/can')
| -rw-r--r-- | drivers/net/can/c_can/c_can.c | 22 |
1 files changed, 12 insertions, 10 deletions
diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c index 77061eebb034..951bfede8f3d 100644 --- a/drivers/net/can/c_can/c_can.c +++ b/drivers/net/can/c_can/c_can.c @@ -808,17 +808,19 @@ static int c_can_do_rx_poll(struct net_device *dev, int quota) u32 num_rx_pkts = 0; unsigned int msg_obj, msg_ctrl_save; struct c_can_priv *priv = netdev_priv(dev); - u32 val = c_can_read_reg32(priv, C_CAN_INTPND1_REG); + u16 val; + + /* + * It is faster to read only one 16bit register. This is only possible + * for a maximum number of 16 objects. + */ + BUILD_BUG_ON_MSG(C_CAN_MSG_OBJ_RX_LAST > 16, + "Implementation does not support more message objects than 16"); + + while (quota > 0 && (val = priv->read_reg(priv, C_CAN_INTPND1_REG))) { + while ((msg_obj = ffs(val)) && quota > 0) { + val &= ~BIT(msg_obj - 1); - for (msg_obj = C_CAN_MSG_OBJ_RX_FIRST; - msg_obj <= C_CAN_MSG_OBJ_RX_LAST && quota > 0; - val = c_can_read_reg32(priv, C_CAN_INTPND1_REG), - msg_obj++) { - /* - * as interrupt pending register's bit n-1 corresponds to - * message object n, we need to handle the same properly. - */ - if (val & (1 << (msg_obj - 1))) { c_can_object_get(dev, 0, msg_obj, IF_COMM_ALL & ~IF_COMM_TXRQST); msg_ctrl_save = priv->read_reg(priv, |