netdev - Re: [PATCH net-next] softirq: reduce latencies

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Date:	Thu, 03 Jan 2013 05:31:59 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	sedat.dilek@...il.com
Cc:	netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] softirq: reduce latencies

On Thu, 2013-01-03 at 14:12 +0100, Sedat Dilek wrote:
> Hi Eric,
> 
> your patch from [2] applies cleanly on top of Linux v3.8-rc2.
> I would like to test it.
> In [1] you were talking about benchmarks you did.
> Can you describe them or provide a testcase (script etc.)?
> You made only network testing?

Yes I did network testing : 

- net_rx_action() softirq handler is the typical function that can
consume 2 ms per call.

I did some netperf sessions, with multiqueue 10G nics, tuned to that IRQ
would be handled by few cpus.
 (check /proc/irq/*/eth0-$QUEUE/../smp_affinity )

Another way to make the softirq processing use more cpu cycles is by
adding a fake iptable setup like :

for n in `seq 1 100`
do
 iptables -I INPUT
done

A common network load is to launch ~200 concurrent TCP_RR netperf
sessions like the following

netperf -H remote_host -t TCP_RR -l 1000

And then you can launch some netperf asking P99_LATENCY results :

netperf -H remote_host -t TCP_RR -- -k P99_LATENCY

You can play with taskset or netperf option -T to force
netperf/netserver running on given cpus.



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