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@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
And make sure you disabled hardware rxhash (if your NIC provides it)
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