On 11.04.2012 13:00, Luigi Rizzo wrote:
On Wed, Apr 11, 2012 at 12:35:10PM +0200, Andre Oppermann wrote:
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.
so you suggest that the (de)scheduling is costing several microseconds ?
Not directly. I'm just trying to explain what's going on to
get a better idea where it may go wrong.
There may be a poor ISR/scheduler interaction that prevents that
causes the packet to be processed only on the next tick or something
like that. I don't have a better explanation for this.
Do we have something like yield() to measure how expensive is the
scheduler ? I ran some tests in a distant past and i remember numbers
of a few microseconds, but that was almost two gigahertz ago...
--
Andre
_______________________________________________
freebsd-current@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-current
To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
