From owner-freebsd-net@FreeBSD.ORG Fri Oct 21 06:07:03 2005 Return-Path: X-Original-To: freebsd-net@FreeBSD.org Delivered-To: freebsd-net@FreeBSD.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id E7A1516A41F; Fri, 21 Oct 2005 06:07:03 +0000 (GMT) (envelope-from yar@comp.chem.msu.su) Received: from comp.chem.msu.su (comp.chem.msu.su [158.250.32.97]) by mx1.FreeBSD.org (Postfix) with ESMTP id 8246F43D45; Fri, 21 Oct 2005 06:07:00 +0000 (GMT) (envelope-from yar@comp.chem.msu.su) Received: from comp.chem.msu.su (localhost [127.0.0.1]) by comp.chem.msu.su (8.13.3/8.13.3) with ESMTP id j9L66tC7097011; Fri, 21 Oct 2005 10:06:55 +0400 (MSD) (envelope-from yar@comp.chem.msu.su) Received: (from yar@localhost) by comp.chem.msu.su (8.13.3/8.13.3/Submit) id j9L66t4j097010; Fri, 21 Oct 2005 10:06:55 +0400 (MSD) (envelope-from yar) Date: Fri, 21 Oct 2005 10:06:55 +0400 From: Yar Tikhiy To: Gleb Smirnoff , freebsd-net@FreeBSD.org, ru@FreeBSD.org, Andrew Thompson Message-ID: <20051021060654.GC69814@comp.chem.msu.su> References: <20051019102559.GA45909@heff.fud.org.nz> <20051020070054.GZ59364@cell.sick.ru> <20051020085721.GC27114@comp.chem.msu.su> <20051021053033.GW59364@cell.sick.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20051021053033.GW59364@cell.sick.ru> User-Agent: Mutt/1.5.9i Cc: Subject: Re: vlan patch X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 21 Oct 2005 06:07:04 -0000 On Fri, Oct 21, 2005 at 09:30:33AM +0400, Gleb Smirnoff wrote: > On Thu, Oct 20, 2005 at 12:57:21PM +0400, Yar Tikhiy wrote: > Y> The hash code consists of literally a couple of #define's. And the > Y> difference between ng_vlan(4) and vlan(4) is that each ng_vlan node > Y> gets its own instance of the hash table. OTOH, in vlan(4) we need > Y> to decide if the hash table will be per parent interface or a single > Y> global instance. In the latter case we could hash by a combination > Y> of the VLAN tag and parent's ifindex. Perhaps this approach will > Y> yield more CPU cache hits during hash table lookups. In addition, > Y> it will be thriftier in using memory. Locking the global hash table > Y> should not be an issue as we can use an sx lock in this case for > Y> optimal read access. > > The sx lock is slow. We'd better use per interface hash, and thus > get locking instantly, with per-vlan lock. In other case, we will > acquire per-vlan lock + the sx lock on every packet. The sx lock > actually means mtx_lock+mtx_unlock, thus we will make 3 mutex > operations instead of one. OK, let's forget about sx locks. However, a per-interface hash is associated with a _physical_ interface, hence we must find the vlan to lock using the hash first. If there were a physical interface lock held by its driver in each case, it could protect the hash as well. Can we rely on this? -- Yar