* [PATCH] can: c_can: Speed up rx_poll function
@ 2013-10-28 16:59 Markus Pargmann
2013-10-28 17:12 ` Joe Perches
0 siblings, 1 reply; 3+ messages in thread
From: Markus Pargmann @ 2013-10-28 16:59 UTC (permalink / raw)
To: Marc Kleine-Budde, Wolfgang Grandegger
Cc: linux-can, netdev, linux-kernel, kernel, Markus Pargmann
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 loops 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 find_next_bit 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 63939 4268457 us 66.758 us 818790.9 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 103034 24220362 us 235.071 us 6016656 us
Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
---
drivers/net/can/c_can/c_can.c | 30 ++++++++++++++++++++----------
1 file changed, 20 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..31af033 100644
--- a/drivers/net/can/c_can/c_can.c
+++ b/drivers/net/can/c_can/c_can.c
@@ -259,6 +259,12 @@ static u32 c_can_read_reg32(struct c_can_priv *priv, enum reg index)
return val;
}
+u16 c_can_read_reg16(struct c_can_priv *priv, enum reg index)
+{
+ u16 val = priv->read_reg(priv, index);
+ return val;
+}
+
static void c_can_enable_all_interrupts(struct c_can_priv *priv,
int enable)
{
@@ -798,17 +804,21 @@ 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);
+ unsigned long val = c_can_read_reg16(priv, C_CAN_INTPND1_REG);
+
+ /*
+ * 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 = c_can_read_reg16(priv, C_CAN_INTPND1_REG))) {
+ msg_obj = 0;
+ while ((msg_obj = find_next_bit(&val, 16, msg_obj)) < 16 &&
+ quota > 0) {
+ ++msg_obj;
- 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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] can: c_can: Speed up rx_poll function
2013-10-28 16:59 [PATCH] can: c_can: Speed up rx_poll function Markus Pargmann
@ 2013-10-28 17:12 ` Joe Perches
2013-10-28 18:28 ` Markus Pargmann
0 siblings, 1 reply; 3+ messages in thread
From: Joe Perches @ 2013-10-28 17:12 UTC (permalink / raw)
To: Markus Pargmann
Cc: Marc Kleine-Budde, Wolfgang Grandegger, linux-can, netdev,
linux-kernel, kernel
On Mon, 2013-10-28 at 17:59 +0100, Markus Pargmann wrote:
> This patch speeds up the rx_poll function by reducing the number of
> register reads.
trivial notes:
> diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c
[]
> @@ -259,6 +259,12 @@ static u32 c_can_read_reg32(struct c_can_priv *priv, enum reg index)
> +u16 c_can_read_reg16(struct c_can_priv *priv, enum reg index)
> +{
> + u16 val = priv->read_reg(priv, index);
> + return val;
> +}
This function doesn't seem useful at all.
It's not exported and it's not static.
Why not use an in-place priv->read_reg(priv, index)?
> +
> static void c_can_enable_all_interrupts(struct c_can_priv *priv,
> int enable)
> {
> @@ -798,17 +804,21 @@ 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);
> + unsigned long val = c_can_read_reg16(priv, C_CAN_INTPND1_REG);
Probably better as a u16 as detailed below.
> + /*
> + * 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 = c_can_read_reg16(priv, C_CAN_INTPND1_REG))) {
> + msg_obj = 0;
> + while ((msg_obj = find_next_bit(&val, 16, msg_obj)) < 16 &&
Using ffs instead of find_next_bit would be more standard
and probably faster too.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] can: c_can: Speed up rx_poll function
2013-10-28 17:12 ` Joe Perches
@ 2013-10-28 18:28 ` Markus Pargmann
0 siblings, 0 replies; 3+ messages in thread
From: Markus Pargmann @ 2013-10-28 18:28 UTC (permalink / raw)
To: Joe Perches
Cc: Marc Kleine-Budde, Wolfgang Grandegger, linux-can, netdev,
linux-kernel, kernel
On Mon, Oct 28, 2013 at 10:12:16AM -0700, Joe Perches wrote:
> On Mon, 2013-10-28 at 17:59 +0100, Markus Pargmann wrote:
> > This patch speeds up the rx_poll function by reducing the number of
> > register reads.
>
> trivial notes:
>
> > diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c
> []
> > @@ -259,6 +259,12 @@ static u32 c_can_read_reg32(struct c_can_priv *priv, enum reg index)
> > +u16 c_can_read_reg16(struct c_can_priv *priv, enum reg index)
> > +{
> > + u16 val = priv->read_reg(priv, index);
> > + return val;
> > +}
>
> This function doesn't seem useful at all.
> It's not exported and it's not static.
Oh right, should be static.
>
> Why not use an in-place priv->read_reg(priv, index)?
No reason for that. Especially with a u16 as mentioned below, it is
clear enough that we have a 16bit value, so I will change it.
>
> > +
> > static void c_can_enable_all_interrupts(struct c_can_priv *priv,
> > int enable)
> > {
> > @@ -798,17 +804,21 @@ 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);
> > + unsigned long val = c_can_read_reg16(priv, C_CAN_INTPND1_REG);
>
> Probably better as a u16 as detailed below.
>
> > + /*
> > + * 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 = c_can_read_reg16(priv, C_CAN_INTPND1_REG))) {
> > + msg_obj = 0;
> > + while ((msg_obj = find_next_bit(&val, 16, msg_obj)) < 16 &&
>
> Using ffs instead of find_next_bit would be more standard
> and probably faster too.
I wasn't aware of that. I will change it
Thanks,
Markus Pargmann
--
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Industrial Linux Solutions | http://www.pengutronix.de/ |
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