Re: questions on NAPI processing latency and dropped network packets

[Eric Dumazet]

Chris Friesen a écrit :
> Eric Dumazet wrote:
> > Chris Friesen a écrit :
> >
> > > I've done some further digging, and it appears that one of the 
> > > problems we may be facing is very high instantaneous traffic rates.
> > >
> > > Instrumentation showed up to 222K packets/sec for short periods (at 
> > > least 1.1 ms, possibly longer), although the long-term average is 
> > > down around 14-16K packets/sec.
> >
> >
> > Instrumentation done where exactly ?
>
> I added some code to e1000_clean_rx_irq() to track rx_fifo drops, total 
> packets received, and an accurate timestamp.
>
> If rx_fifo errors changed, it would dump the information.
>
> > > Is there anything else we can do to minimize the latency of network 
> > > packet processing and avoid having to crank the rx ring size up so high?
>
> > You have some tasks that disable softirqs too long. Sometimes, bumping 
> > RX ring size is OK (but you will still have delays), sometimes it is 
> > not an option, since 4096 is the limit on current hardware.
>
> I added some instrumentation to take timestamps in __do_softirq() as 
> well.  Based on these timestamps, I can see the following code sequence:
>
> 2374604616 usec, start processing softirqs in __do_softirq()
> 2374610337 usec, log values in e1000_clean_rx_irq()
> 2374611411 usec, log values in e1000_clean_rx_irq()
>
> In between the successive calls to e1000_clean_rx_irq() the rx_fifo 
> counts went up.
>
> Does anyone have any patchsets to track down what softirqs are taking a 
> long time, and/or who's disabling softirqs?

Not for linux-2.6.10 unfortunatly.

Check net/ipv4/route.c, where many improvements can be done, especially if you 
have a large rt cache

grep . /proc/sys/net/ipv4/route/*

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