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Date: Mon, 30 Mar 2015 10:51:51 +0200
From: Hans Petter Selasky <hps@selasky.org>
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To: Ian Lepore <ian@freebsd.org>, Gleb Smirnoff <glebius@FreeBSD.org>
Subject: Re: svn commit: r280759 - head/sys/netinet
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Cc: "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>,
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Hi,

Like was mentioned here, maybe we need a global counter that is not 
accessed that frequently, and use per-cpu counters for the most frequent 
accesses. To keep the order somewhat sane, we need a global counter:

Pseudo code:

static int V_ip_id;

PER_CPU(V_ip_id_start);
PER_CPU(V_ip_id_end);

static uint16_t
get_next_id()
{
if (PER_CPU(V_ip_id_start) == PER_CPU(V_ip_id_end)) {
	next = atomic_add32(&V_ip_id, 256);
	V_ip_id_start = next;
	V_ip_id_end = next + 256;
}
id = V_ip_id_start++;
return (id);
}

--HPS