On Tue, Dec 10, 2002 at 02:09:12PM +0100, Stephan von Krawczynski wrote: > Well, what I am trying to say is this: my experience is that under load with > small sized packets even standard routing/packet forwarding becomes lossy. This is more often dependant on hardware itself (NICs, chipsets). When your NIC doesn't support scatter/gather, mitigated interrupts and other wonderful features, and it receives 148600 pkts/second, it generates as many interrupts. Many chipsets completely die under such a load. I can tell you that I wasn't proud of hanging my Dual Athlon 1800+ with its 64/66 PCI slots and so from a single Celeron 800 on 100 Mbps copper ! > If I put NAT and other nice netfilter features on top of such a situation things > get a lot worse (obviously) - no comparison to building the "application" (e.g. > cluster) with routing and hidden-patch (mainly because of its pure simplicity I > guess). don't even need that to kill a system. Only a cheap NIC, a responding MAC address and that's all. Of course routing make it worse and NAT even more. And BTW, when I get 10 to 12 kHits/s with Tux on a 100 Mbps network, you'll notice that it only happens on empty files. This is about 1 kB per hit, from a wire point of vue. Count the ACKs, the data (tcp headers), and global overhead, and you're not far from wire-speed on very small packets. > Don't get me wrong: I am pretty content with the hidden-patch and my setup > without NAT. But I wanted to point to the direction of possible further routing > performance improvement in 2.4.X tree. Is it correct that I can expect higher > data-rates (concerning small packets) if using higher HZ ? don't know. perhaps forwarding packets between input and output involves queues that are processed alternatively at HZ rate, but that seems strange to me. > Someone selling E3 cards told me he cannot manage loads like these (small > packet stuff) with a stock kernel, and that you _at least_ have to increase HZ > to get acceptable throughput results. E3 is only 45 Mbps (or I'm mistaken) ? Tweaking such parameters for such medium rates doesn't seem the most appropriate to me. Perhaps his driver has some problems. Cheers, Willy - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
