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From: Juli Mallett <jmallett@freebsd.org>
Date: Tue, 27 Dec 2011 22:32:13 -0800
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Cc: Pawel Tyll <ptyll@nitronet.pl>,
	"Alexander V. Chernikov" <melifaro@freebsd.org>,
	Luigi Rizzo <rizzo@iet.unipi.it>, freebsd-ipfw@freebsd.org,
	freebsd-net@freebsd.org
Subject: Re: Firewall Profiling.
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2011/12/27 Lev Serebryakov <lev@freebsd.org>:
> Hello, Luigi.
> You wrote 27 =D0=B4=D0=B5=D0=BA=D0=B0=D0=B1=D1=80=D1=8F 2011 =D0=B3., 18:=
26:00:
>
>> plans, yes - not sure how long it will take. I have compiled
>> ipfw+dummynet as a standalone module (outside the kernel)
>> but have not yet hooked the code to netmap to figure out how fast
>> it can run.
> =C2=A0I still don't understand why it should be faster than "normal" way,
> as it is essentially same (ipfw + dummynet) code + some additional
> context switches for netmap (to userland and back).
> =C2=A0What does netmap shave off from packet processing in this particula=
r
> case, to compensate context switches? I

Reloading of mbufs into DMA descriptors?  mbuf allocator overhead
itself?  Interrupts.  Context switches under constant heavy load.
Some indirection in the network stack.