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SubjectRe: NAPI and tg3

Steffen Persvold writes:

> True, but it doesn't say that if you have two applications loaded on
> a SMP box, one which is for example constantly receiving and sending data
> from/to the network and doing computations on the data (100 % CPU) while
> some other app is only doing computations (also 100 % CPU), the ksoftirqd
> which should receive packets and refill the TX and RX rings will be put
> last in the queue because of its low nice level (19), thus the network
> dependent application has very much lower performance than what could be
> achieved with a nice level of 0 or even running the interrupt based
> mechanism. A nice level of 0 on ksoftirqd is still a heck of a lot better
> than interrupt context isn't it ?

Yes my scripts test/production has even been setting -19 to ksoftirq just
for that reason so I almost forgot this issue so I'm happy you brought
this up. But dev->poll is not the only user of ksoftirq but for heavy
networking it's gets pretty dominant. So we add something to NAPI_HOWTO
and pass the question about ksoftirq default priority to others.

From a GIGE router in production.

root 3 0.2 0.0 0 0 ? RWN Aug 15 602:00 (ksoftirqd_CPU0)
root 232 0.0 7.9 41400 40884 ? S Aug 15 74:12 gated

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