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Date: Sat, 14 Sep 2013 16:25:26 +0200
From: Luigi Rizzo <rizzo@iet.unipi.it>
To: George Neville-Neil <gnn@neville-neil.com>
Subject: Re: Network stack changes
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Cc: "Alexander V. Chernikov" <melifaro@yandex-team.ru>,
 Adrian Chadd <adrian@freebsd.org>, Andre Oppermann <andre@freebsd.org>,
 "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>,
 "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org>,
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 FreeBSD Net <net@freebsd.org>
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On Fri, Sep 13, 2013 at 11:08:27AM -0400, George Neville-Neil wrote:
> 
> On Aug 29, 2013, at 7:49 , Adrian Chadd <adrian@freebsd.org> wrote:
...
> One quick note here.  Every time you increase batching you may increase bandwidth
> but you will also increase per packet latency for the last packet in a batch.

The ones who suffer are the first ones, because their processing
is somewhat delayed to 1) let the input batch build up, and 2) complete
processing of the batch before pushing results to the next stage.

However one should never wait for an input batch to grow; you process
whatever your source gives you (one or more packets)
by the time you are ready (and if you are slow/overloaded, of course
you will get a large backlog at once). Either way, there is no
reason to create additional delay on input.

cheers
luigi