Date: Thu, 20 Oct 2005 11:00:54 +0400 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Andrew Thompson <thompsa@FreeBSD.org> Cc: freebsd-net@FreeBSD.org, yar@FreeBSD.org, ru@FreeBSD.org Subject: Re: vlan patch Message-ID: <20051020070054.GZ59364@cell.sick.ru> In-Reply-To: <20051019102559.GA45909@heff.fud.org.nz> References: <20051019102559.GA45909@heff.fud.org.nz>
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Andrew, On Wed, Oct 19, 2005 at 11:25:59PM +1300, Andrew Thompson wrote: A> It has always bugged me how the vlan code traverses the linked-list for A> each incoming packet to find the right ifvlan, I have this patch which A> attempts to fix this. A> A> What it does is replace the linear search for the vlan with a constant A> time lookup. It does this by allocating an array for each vlan enabled A> parent interface so the tag can be directly indexed. A> A> This has an overhead of ~16kb on 32bit, this is not too bad as there is A> usually only one physical interface when using a large number of vlans. A> A> I have measured a 1.6% pps increase with 100 vlans, and 8% with 500, and A> yes, some people use this many in production. A> A> It also has the benefit of enforcing unique vlan tags per parent which A> the current code doesn't do. Although the memory overhead is not noticable on modern i386 and amd64 PCs I don't think that we should waste so much memory. We should keep in mind the existence of embedded architectures with little memory. In most cases people use 10 - 30 VLANs. I suggest to use a hash, like it is already done in ng_vlan(4). This hash makes every sixteenth VLAN to fall into same slot. Since most people allocate VLAN ids contiguously the hash distribution should be good. Moreover, I suggest Yar and Ruslan to work together and make the hash code shared between vlan(4) and ng_vlan(4), not copy-and-pasted. -- Totus tuus, Glebius. GLEBIUS-RIPN GLEB-RIPE
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