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Subject[PATCH] USB speedtouch: send path optimization
Date
Write multiple cells in one function call, rather than one cell per
function call. Under maximum send load, this reduces cell writing
CPU usage from 0.0095% to 0.0085% on my machine. A 10% improvement! :)


speedtouch.c | 68 +++++++++++++++++++++++++++++++++++------------------------
1 files changed, 41 insertions(+), 27 deletions(-)


diff -Nru a/drivers/usb/misc/speedtouch.c b/drivers/usb/misc/speedtouch.c
--- a/drivers/usb/misc/speedtouch.c Mon Mar 10 10:35:23 2003
+++ b/drivers/usb/misc/speedtouch.c Mon Mar 10 10:35:23 2003
@@ -273,39 +273,60 @@
ctrl->aal5_trailer [7] = crc;
}

-static char *udsl_write_cell (struct sk_buff *skb, char *target) {
+unsigned int udsl_write_cells (unsigned int howmany, struct sk_buff *skb, unsigned char **target_p) {
struct udsl_control *ctrl = UDSL_SKB (skb);
+ unsigned char *target = *target_p;
+ unsigned int nc, ne, i;

- ctrl->num_cells--;
+ dbg ("udsl_write_cells: howmany=%u, skb->len=%d, num_cells=%u, num_entire=%u, pdu_padding=%u", howmany, skb->len, ctrl->num_cells, ctrl->num_entire, ctrl->pdu_padding);

- memcpy (target, ctrl->cell_header, ATM_CELL_HEADER);
- target += ATM_CELL_HEADER;
+ nc = ctrl->num_cells;
+ ne = min (howmany, ctrl->num_entire);

- if (ctrl->num_entire) {
- ctrl->num_entire--;
+ for (i = 0; i < ne; i++) {
+ memcpy (target, ctrl->cell_header, ATM_CELL_HEADER);
+ target += ATM_CELL_HEADER;
memcpy (target, skb->data, ATM_CELL_PAYLOAD);
target += ATM_CELL_PAYLOAD;
__skb_pull (skb, ATM_CELL_PAYLOAD);
- return target;
}

+ ctrl->num_entire -= ne;
+
+ if (!(ctrl->num_cells -= ne) || !(howmany -= ne))
+ goto out;
+
+ memcpy (target, ctrl->cell_header, ATM_CELL_HEADER);
+ target += ATM_CELL_HEADER;
memcpy (target, skb->data, skb->len);
target += skb->len;
__skb_pull (skb, skb->len);
-
memset (target, 0, ctrl->pdu_padding);
target += ctrl->pdu_padding;

- if (ctrl->num_cells) {
- ctrl->pdu_padding = ATM_CELL_PAYLOAD - ATM_AAL5_TRAILER;
- } else {
- memcpy (target, ctrl->aal5_trailer, ATM_AAL5_TRAILER);
- target += ATM_AAL5_TRAILER;
- /* set pti bit in last cell */
- *(target + 3 - ATM_CELL_SIZE) |= 0x2;
+ if (--ctrl->num_cells) {
+ if (!--howmany) {
+ ctrl->pdu_padding = ATM_CELL_PAYLOAD - ATM_AAL5_TRAILER;
+ goto out;
+ }
+
+ memcpy (target, ctrl->cell_header, ATM_CELL_HEADER);
+ target += ATM_CELL_HEADER;
+ memset (target, 0, ATM_CELL_PAYLOAD - ATM_AAL5_TRAILER);
+ target += ATM_CELL_PAYLOAD - ATM_AAL5_TRAILER;
+
+ if (--ctrl->num_cells)
+ BUG();
}

- return target;
+ memcpy (target, ctrl->aal5_trailer, ATM_AAL5_TRAILER);
+ target += ATM_AAL5_TRAILER;
+ /* set pti bit in last cell */
+ *(target + 3 - ATM_CELL_SIZE) |= 0x2;
+
+out:
+ *target_p = target;
+ return nc - ctrl->num_cells;
}


@@ -500,14 +521,12 @@
static void udsl_process_send (unsigned long data)
{
struct udsl_send_buffer *buf;
- unsigned int cells_to_write;
int err;
unsigned long flags;
- unsigned int i;
struct udsl_instance_data *instance = (struct udsl_instance_data *) data;
+ unsigned int num_written;
struct sk_buff *skb;
struct udsl_sender *snd;
- unsigned char *target;

dbg ("udsl_process_send entered");

@@ -577,16 +596,11 @@
instance->current_buffer = buf;
}

- cells_to_write = min (buf->free_cells, UDSL_SKB (skb)->num_cells);
- target = buf->free_start;
-
- dbg ("writing %u cells from skb 0x%p to buffer 0x%p", cells_to_write, skb, buf);
+ num_written = udsl_write_cells (buf->free_cells, skb, &buf->free_start);

- for (i = 0; i < cells_to_write; i++)
- target = udsl_write_cell (skb, target);
+ dbg ("wrote %u cells from skb 0x%p to buffer 0x%p", num_written, skb, buf);

- buf->free_start = target;
- if (!(buf->free_cells -= cells_to_write)) {
+ if (!(buf->free_cells -= num_written)) {
list_add_tail (&buf->list, &instance->filled_buffers);
instance->current_buffer = NULL;
dbg ("queued filled buffer");
-
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