From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH net-next] net: bridge: use rhashtable for fdbs Date: Tue, 12 Dec 2017 10:07:13 -0800 Message-ID: <20171212100713.6c24c9c3@xeon-e3> References: <1513087370-4791-1-git-send-email-nikolay@cumulusnetworks.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, bridge@lists.linux-foundation.org, roopa@cumulusnetworks.com, srn@prgmr.com, davem@davemloft.net To: Nikolay Aleksandrov Return-path: Received: from mail-pg0-f66.google.com ([74.125.83.66]:33478 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752609AbdLLSHP (ORCPT ); Tue, 12 Dec 2017 13:07:15 -0500 Received: by mail-pg0-f66.google.com with SMTP id g7so13950333pgs.0 for ; Tue, 12 Dec 2017 10:07:15 -0800 (PST) In-Reply-To: <1513087370-4791-1-git-send-email-nikolay@cumulusnetworks.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 12 Dec 2017 16:02:50 +0200 Nikolay Aleksandrov wrote: > Before this patch the bridge used a fixed 256 element hash table which > was fine for small use cases (in my tests it starts to degrade > above 1000 entries), but it wasn't enough for medium or large > scale deployments. Modern setups have thousands of participants in a > single bridge, even only enabling vlans and adding a few thousand vlan > entries will cause a few thousand fdbs to be automatically inserted per > participating port. So we need to scale the fdb table considerably to > cope with modern workloads, and this patch converts it to use a > rhashtable for its operations thus improving the bridge scalability. > Tests show the following results (10 runs each), at up to 1000 entries > rhashtable is ~3% slower, at 2000 rhashtable is 30% faster, at 3000 it > is 2 times faster and at 30000 it is 50 times faster. > Obviously this happens because of the properties of the two constructs > and is expected, rhashtable keeps pretty much a constant time even with > 10000000 entries (tested), while the fixed hash table struggles > considerably even above 10000. > As a side effect this also reduces the net_bridge struct size from 3248 > bytes to 1344 bytes. Also note that the key struct is 8 bytes. > > Signed-off-by: Nikolay Aleksandrov > --- Thanks for doing this, it was on my list of things that never get done. Some downsides: * size of the FDB entry gets larger. * you lost the ability to salt the hash (and rekey) which is important for DDoS attacks * being slower for small (<10 entries) also matters and is is a common use case for containers.