netdev - Re: [PATCH net-next-2.6] net: speedup udp receive path

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Date:	Sat, 01 May 2010 12:47:29 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	hadi@...erus.ca, David Miller <davem@...emloft.net>,
	therbert@...gle.com, shemminger@...tta.com, netdev@...r.kernel.org,
	Eilon Greenstein <eilong@...adcom.com>,
	Brian Bloniarz <bmb@...enacr.com>
Subject: Re: [PATCH net-next-2.6] net: speedup udp receive path

Le samedi 01 mai 2010 à 18:24 +0800, Changli Gao a écrit :
> On Sat, May 1, 2010 at 2:14 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> > BTW, using ee mask, cpu4 is not used at _all_, even for the user
> > threads. Scheduler does a bad job IMHO.
> >
> > Using fe mask, I get all packets (sent at 733311pps by my pktgen
> > machine), and my CPU0 even has idle time !!!
> >
> > Limit seems to be around 800.000 pps
> >
> > ------------------------------------------------------------------------------------------------------------------------
> >   PerfTop:    5616 irqs/sec  kernel:93.9% [1000Hz cycles],  (all, 8 CPUs)
> > ------------------------------------------------------------------------------------------------------------------------
> >
> 
> Oh, cpu0 usage is about 100-(100-93.9)*8 = 51.2%(Am I right?). If we
> can do weighted packet distributing: cpu0's weight is 1, and other
> cpus are 2. maybe we can utilize all the cpu power.
> 

Nope, cpu0 was at 100% in this test, other cpus were about at 50% each.

weigthed would be ok if I wanted to use cpu0 in the 'slave' cpus (RPS
targets). But I know the workload I am interested to, and ability to
resist to DDOS, want to keep cpu0 outside of IP/TCP/UDP stack.


Later, skb_pull() inline in eth_type_trans() permitted to reach 840.000
pps.

top - 12:42:55 up  3:00,  2 users,  load average: 0.44, 0.11, 0.03
Tasks: 126 total,   1 running, 125 sleeping,   0 stopped,   0 zombie
Cpu(s):  2.2%us, 16.5%sy,  0.0%ni, 46.5%id, 11.4%wa,  0.9%hi, 22.5%si,
0.0%st
Mem:   4148112k total,   211152k used,  3936960k free,    15228k buffers
Swap:  4192928k total,        0k used,  4192928k free,   121804k cached

You can see average idle of 46%
So there is probably more optimizations to do to reach maybe 1.300.000
pps ;)



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