netdev - Re: [PATCH v3] net: batch skb dequeueing from softnet input_pkt

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Date:	Wed, 14 Apr 2010 08:28:21 -0400
From:	jamal <hadi@...erus.ca>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v3] net: batch skb dequeueing from softnet
 input_pkt_queue

On Wed, 2010-04-14 at 20:13 +0800, Changli Gao wrote:
> On Wed, Apr 14, 2010 at 7:58 PM, jamal <hadi@...erus.ca> wrote:

> No extra IPI is needed.
> 
> +       qlen = queue->input_pkt_queue.qlen + queue->processing_queue.qlen;
> +       if (qlen <= netdev_max_backlog) {
> +               if (qlen) {
> 
> the packets in processing_queue are counted too.

Ok - Looks reasonable.

> > IPIs add to latency (refer to my other email). Did you test this
> > to reach some conclusion that it improves thing or was it just by
> > inspection?
> >
> 
> :( only insepection.

I am probably being pushy, but one simple test for latency of single
flow is: 

from machine 1, send ping -f

on rps machine:
Base test: no rps on ( a fresh boot with no sysctls should do fine)
Test 1: irq affinity on cpuX, rps to cpuY 
Test 2: repeat test1 with your change.

It should show no difference between test1 and 2. If it shows
improvement better - but showing worse latency is bad.

cheers,
jamal

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