fre, 28 08 2009 kl. 16:41 +0200, skrev Johannes Stezenbach: > On Thu, Aug 20, 2009 at 02:56:49PM +0200, Johannes Stezenbach wrote: > > On Wed, Aug 19, 2009 at 04:35:34PM +0100, Jamie Lokier wrote: > > > Johannes Stezenbach wrote: > > > > > > > > TCP RX ~70Mbit/sec (iperf -s on SoC, iperf -c on destop PC) > > > > TCP TX ~56Mbit/sec (iperf -s on destop PC, iperf -c o SoC) > > > > > > > > The CPU load during the iperf test is around > > > > 1% user, 44% system, 4% irq, 48% softirq, with 7500 irqs/sec. > > > > > > > > The kernel used in these measurements does not have iptables > > > > support, I think packet filtering will slow it down noticably, > > > > but I didn't actually try. The ethernet driver uses NAPI, > > > > but it doesn't seem to be a win judging from the irq/sec number. > > > > > > You should see far fewer interrupts if NAPI was working properly. > > > Rather than NAPI not being a win, it looks like it's not active at > > > all. > > > > > > 7500/sec is close to the packet rate, for sending TCP with > > > full-size ethernet packages over a 100Mbit ethernet link. > > > > From debug output I can see that NAPI works in principle, however > > the timing seems to be such that ->poll() almost always completes > > before the next packet is received. I followed the NAPI_HOWTO.txt > > which came with the 2.6.20 kernel. The delay between irq -> > > netif_rx_schedule() -> NET_RX_SOFTIRQ -> ->poll() doesn't seem > > to be long enough. But of course my understanding of NAPI is > > very limited, probably I missed something... > > It would've been nice to get a comment on this. Yeah I know, > old kernel, non-mainline driver... Tried porting the driver to mainline? That way you will get more than two years of improvements to the networking stack including NAPI. There was a rework of NAPI [1] around 2.6.24, you'd probably like to see commit bea3348eef27e6044b6161fd04c3152215f96411. You could also ask the linux driver project to help you make the driver suitable for mainline inclusion. [1] http://lwn.net/Articles/244640/ Simon Holm Thøgersen -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
