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Message-Id: <1383298596-18385-1-git-send-email-mpa@pengutronix.de>
Date: Fri, 1 Nov 2013 10:36:36 +0100
From: Markus Pargmann <mpa@...gutronix.de>
To: Marc Kleine-Budde <mkl@...gutronix.de>,
Wolfgang Grandegger <wg@...ndegger.com>
Cc: Joe Perches <joe@...ches.com>, linux-can@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel@...gutronix.de, Markus Pargmann <mpa@...gutronix.de>
Subject: [PATCH v3] 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@...gutronix.de>
---
Notes:
Changes in v3:
- Update commit message (measurements and ffs)
Changes in v2:
- Small changes, find_next_bit -> ffs and other
drivers/net/can/c_can/c_can.c | 22 ++++++++++++----------
1 file 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 a668cd4..428681e 100644
--- a/drivers/net/can/c_can/c_can.c
+++ b/drivers/net/can/c_can/c_can.c
@@ -798,17 +798,19 @@ 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,
--
1.8.4.rc3
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