On Sat, Aug 19, 2006 at 02:33:42PM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2006-08-18 at 18:45 -0500, Linas Vepstas wrote:
> > On Fri, Aug 18, 2006 at 06:29:42PM -0500, linas wrote:
> > >
> > > I don't understand what you are saying. If I call the transmit
> > > queue cleanup code from the poll() routine, nothing hapens,
> > > because the kernel does not call the poll() routine often
> > > enough. I've stated this several times.
> >
> > OK, Arnd gave me a clue stick. I need to call the (misnamed)
> > netif_rx_schedule() from the tx interrupt in order to get
> > this to work. That makes sense, and its easy, I'll send the
> > revised patch.. well, not tonight, but shortly.
>
> You might not want to call it all the time though... You need some
> interrupt mitigation and thus a timer that calls netif_rx_schedule()
> might be of some use still...
Well, again, the whole point of a low-watermark interrupt is to
get zero of them when the system is working correctly; they're
self-mitigating by design.
-------------
Anyway, I tried the suggestion, but am getting less-than-ideal
results.
To recap: my original patch did this:
spider_interrupt_handler(struct whatever *) {
...
if (tx_interrupt)
schedule_work (tx_cleanup_handler)
}
which David Miller objected to. Once I understood the why
(sorry for not getting it right away), I then replaced the
above with the below, which is what I think everyone wanted:
spider_interrupt_handler(struct whatever *) {
...
if (tx_interrupt)
netif_rx_schedule(netdev);
}
spidernet_poll(stuct whatever *) {
tx_cleanup_handler(txring);
// rx_stuff too ...
}
I was expecting this to be a no-op from the performance
point of view. Instead, I get a fairly dramatic (11%) slowdown:
the first patch runs in the 785-805 Mbits/sec range, while
the second patch runs in the 705-715 Mbits/sec range.
I am surprised, ad don't understand why this would be so.
For the record, the alternate patch is below.
----
Index: linux-2.6.18-rc2/drivers/net/spider_net.c
===================================================================
--- linux-2.6.18-rc2.orig/drivers/net/spider_net.c 2006-08-21
16:59:33.000000000 -0500
+++ linux-2.6.18-rc2/drivers/net/spider_net.c 2006-08-21 17:15:28.000000000
-0500
@@ -1087,6 +1090,8 @@ spider_net_poll(struct net_device *netde
int packets_to_do, packets_done = 0;
int no_more_packets = 0;
+ spider_net_cleanup_tx_ring(card);
+
packets_to_do = min(*budget, netdev->quota);
while (packets_to_do) {
@@ -1495,16 +1500,16 @@ spider_net_interrupt(int irq, void *ptr,
if (!status_reg)
return IRQ_NONE;
- if (status_reg & SPIDER_NET_RXINT ) {
+ if (status_reg & SPIDER_NET_RXINT) {
spider_net_rx_irq_off(card);
netif_rx_schedule(netdev);
}
- if (status_reg & SPIDER_NET_TXINT ) {
- spider_net_cleanup_tx_ring(card);
- netif_wake_queue(netdev);
- }
- if (status_reg & SPIDER_NET_ERRINT )
+ /* Call rx_schedule from the tx interrupt, so that NAPI poll runs. */
+ if (status_reg & SPIDER_NET_TXINT)
+ netif_rx_schedule(netdev);
+
+ if (status_reg & SPIDER_NET_ERRINT)
spider_net_handle_error_irq(card, status_reg);
/* clear interrupt sources */
-
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