From: Eric Dumazet <eric.dumazet@gmail.com>
To: Bradley Peterson <despite@gmail.com>
Cc: paulus@samba.org, linux-ppp@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: Single core gets pegged on multi-core PPTP server
Date: Fri, 20 Jan 2012 07:16:30 +0100 [thread overview]
Message-ID: <1327040190.4826.7.camel@edumazet-laptop> (raw)
In-Reply-To: <CAJuWrdtDgeCOSEvD-ytfwGj4UQeOtjeqUZd3Y1SLpbbsSvrycg@mail.gmail.com>
Le jeudi 19 janvier 2012 à 16:35 -0600, Bradley Peterson a écrit :
> Hello,
>
> I am trying to test the capacity of a linux PPTP server, both in
> number of connections, and in packets per second. I am using kernel
> 2.6.38.8, with the ppp, pptp, and gre modules, and accel-pptp 0.8.3.
> I have RPS, RFS, and XPS enabled on the network devices for SMP
> support.
>
> But I'm seeing one CPU get pegged out with soft interrupt, while the
> others are almost completely idle.
>
> In my current test, I'm starting 250 pptp connections from another
> server, then running iperf across each connection. The client machine
> pegs out, sure, but I'm surprised the server pegs out a single CPU.
> With RPS, I would expect softirq's to be more balanced.
>
> Where could the bottleneck be? Do all ppp packets need to be
> processed serially?
>
Hmmm, you need a more recent kernel or backport commit
c6865cb3cc6f3c2857fa4c6f5fda2945d70b1e84
rps: Inspect GRE encapsulated packets to get flow hash
Crack open GRE packets in __skb_get_rxhash to compute 4-tuple hash on
in encapsulated packet. Note that this is used only when the
__skb_get_rxhash is taken, in particular only when the device does
not compute provide the rxhash (ie. feature is disabled).
This was tested by creating a single GRE tunnel between two 16 core
AMD machines. 200 netperf TCP_RR streams were ran with 1 byte
request and response size.
Without patch: 157497 tps, 50/90/99% latencies 1250/1292/1364 usecs
With patch: 325896 tps, 50/90/99% latencies 603/848/1169
Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
And make sure you disabled hardware rxhash (if your NIC provides it)
next prev parent reply other threads:[~2012-01-20 6:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-19 22:35 Single core gets pegged on multi-core PPTP server Bradley Peterson
2012-01-19 22:55 ` Emanuil Hristov
2012-01-19 23:28 ` Alexey Osipov
2012-01-20 6:16 ` Eric Dumazet [this message]
2012-01-20 15:20 ` Bradley Peterson
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