lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Tue, 3 Feb 2009 15:12:19 +0300 From: Evgeniy Polyakov <zbr@...emap.net> To: david@...g.hm Cc: Herbert Xu <herbert@...dor.apana.org.au>, Jarek Poplawski <jarkao2@...il.com>, David Miller <davem@...emloft.net>, w@....eu, dada1@...mosbay.com, ben@...s.com, mingo@...e.hu, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, jens.axboe@...cle.com Subject: Re: [PATCH v2] tcp: splice as many packets as possible at once On Tue, Feb 03, 2009 at 05:05:14AM -0800, david@...g.hm (david@...g.hm) wrote: > >Maybe just do not allow jumbo frames when memory is fragmented enough > >and fallback to the smaller MTU in this case? With LRO/GRO stuff there > >should be not that much of the overhead compared to multiple-page > >copies. > > > 1. define 'fragmented enough' When allocator can not provide requested amount of data. > 2. the packet size was already negotiated on your existing connections, > how are you going to change all those on the fly? I.e. MTU can not be changed on-flight? Magic world. > 3. what do you do when a remote system sends you a large packet? drop it > on the floor? We already do just that when jumbo frame can not be allocated :) > having some pool of large buffers to receive into (and copy out of those > buffers as quickly as possible) would cause a performance hit when things > get bad, but isn't that better than dropping packets? It is a solution, but I think it will behave noticebly worse than with decresed MTU. > as for the number of buffers to use. make a reasonable guess. if you only > have a small number of packets around, use the buffers directly, as you > use more of them start copying, as useage climbs attempt to allocate more. > if you can't allocate more (and you have all of your existing ones in use) > you will have to drop the packet, but at that point are you really in any > worse shape than if you didn't have some mechanism to copy out of the > large buffers? That's the main point: how to deal with broken hardware? I think (but have no strong numbers though) that having 6 packets with 1500 MTU combined into GRO/LRO frame will be processed way faster than copying 9k MTU into 3 pages and process single skb. -- Evgeniy Polyakov -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists