Re: Very high bandwith packet based interface and performance problems

Alan Cox (
Wed, 21 Feb 2001 22:07:32 +0000 (GMT)

> that because the kernel was getting 99% of the cpu, the application was
> getting very little, and thus the read wasn't happening fast enough, and

Seems reasonable

> This is NOT what I'm seeing at all.. the kernel load appears to be
> pegged at 100% (or very close to it), the user space app is getting
> enough cpu time to read out about 10-20Mbit, and FURTHERMORE the kernel
> appears to be ACKING ALL the traffic, which I don't understand at all
> (e.g. the transmitter is simply blasting 300MBit of tcp unrestricted)

TCP _requires_ the remote end ack every 2nd frame regardless of progress.

> With udp, we can get the full 300MBit throughput, but only if we shape
> the load to 300Mbit. If we increase the load past 300 MBit, the received
> frames (at the user space udp app) drops to 10-20MBit, again due to
> user-space application scheduling problems.

How is your incoming traffic handled architecturally - irq per packet or
some kind of ring buffer with irq mitigation. Do you know where the cpu
load is - is it mostly the irq servicing or mostly network stack ?

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