Re: strange ping response times...

On 11.04.2012 01:32, Luigi Rizzo wrote:
> On Tue, Apr 10, 2012 at 07:05:00PM -0400, Barney Wolff wrote:
>> CPU cache?
>> Cx states?
>> powerd?
>
> powerd is disabled, and i am going down to C1 at most
> 	>  sysctl -a | grep cx
> 	hw.acpi.cpu.cx_lowest: C1
> 	dev.cpu.0.cx_supported: C1/1 C2/80 C3/104
>
> which shouldn't take so much. Sure, cache matters, but the
> fact is, icmp processing on loopback should occur inline.
>
> unless there is a forced descheduling on a select with timeout>  0
> which would explain the extra few microseconds (and makes me worry
> on how expensive is a scheduling decision...)

Things going through loopback go through a NETISR and may
end up queued to avoid LOR situations.  In addition per-cpu
queues with hash-distribution for affinity may cause your
packet to be processed by a different core.  Hence the additional
delay.

-- 
Andre