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SubjectRe: Gigabit Linux Server Bottlenecks

On 8 Feb 2000, Jes Sorensen wrote:

> Ingo> yep, also with jumbo frames (mtu 9000) there is no problem at
> Ingo> all. Eg. the SysKonnect cards i use do just over 20k IRQs/sec
> Ingo> when i'm saturating 107MB/sec TCP bandwith - this IRQ load is
> Ingo> simply not a problem at all for an APIC controller. I've seen
> Ingo> IRQ rates of 80k/sec as well.
>
> Sorry but thats *BAD* performance by the SK card. I do around 2.5K
> ints/sec with the Alteon when doing 65MB/sec traffic in one direction
> with regular sized frames. The load is maybe not a problem for the
> APIC, but 80k/sec truly sucks for the CPUs considering the number of
> context saves/restores they have to do.

i suspect the difference is that my system is not saturated. (has CPU
cycles left). I'm saturating the TCP pipe (107MB/sec) and the gigabit
card, while you are saturated CPU-power-wise. So it's pretty natural that
if the CPU is too busy processing frames, workload gets clustered up into
bigger chunks. Also, on which side do you have 2.5K ints/sec?

another difference might be TX interrupts - i'm using a TX interrupt per
TX-ed descriptor (this way descriptors get freed up ASAP and the outgoing
pipe can be restarted quickly), but i'll switch to the logic i've added to
eepro100.c: cluster TX interrupts if the queue is not full (there is no
danger of Tx descriptor shortage in this case), and if the queue gets full
then stop the queue until a certain number (# != 1) of descriptors have
been freed. (hysteresis) [There might be some difference in queueing here
since i'm doing this based on Alexey's softnet 'next generation
networking' code.]

if we (or the card) are clustering incoming frames even if load is not
high, thats a latency problem - we want to know about available frames as
soon as possible.

-- mingo


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