Date: Mon, 25 Sep 2017 20:23:43 +0000 From: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net> To: "Stephen Hurd" <shurd@sasktel.net> Cc: "Stephen Hurd" <shurd@FreeBSD.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r323942 - head/sys/net Message-ID: <681F1B2B-1CF6-41AC-9EED-B4790AB7CE95@lists.zabbadoz.net> In-Reply-To: <61486844-e6f1-2607-2113-599ebcb02c58@sasktel.net> References: <201709230135.v8N1ZE6S063264@repo.freebsd.org> <B28D9879-4ECF-43E4-9A58-51F616CEC4BE@lists.zabbadoz.net> <283397c7-a01e-3776-7ed3-b64d68003d0b@sasktel.net> <6F5DC92C-2CF6-4A33-9663-BFECB7DB65F2@lists.zabbadoz.net> <89d68ff8-84ed-83a6-4e77-9a321babe2fe@sasktel.net> <4523452E-79B0-494A-B44F-44DE4B747D69@lists.zabbadoz.net> <61486844-e6f1-2607-2113-599ebcb02c58@sasktel.net>
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On 25 Sep 2017, at 17:04, Stephen Hurd wrote: > Bjoern A. Zeeb wrote: >> On 23 Sep 2017, at 23:46, Stephen Hurd wrote: >> >>> Bjoern A. Zeeb wrote: >>>> On 23 Sep 2017, at 6:32, Stephen Hurd wrote: >>>> >>>>> Bjoern A. Zeeb wrote: >>>>>> On 23 Sep 2017, at 1:35, Stephen Hurd wrote: >>>>>> >>>>>>> Author: shurd >>>>>>> Date: Sat Sep 23 01:35:14 2017 >>>>>>> New Revision: 323942 >>>>>>> URL: https://svnweb.freebsd.org/changeset/base/323942 >>>>>>> >>>>>>> Log: >>>>>>> Chain mbufs before passing to if_input() >>>>>>> >>>>>>> Build a list of mbufs to pass to if_input() after LRO. >>>>>>> Results in >>>>>>> 12% small packet forwarding rate improvement. >> I not saying anything against the change, I am just saying the commit >> message doesn’t describe what it does. > > Can you explain what was confusing about it or propose other wording? > I'm not sure what was confusing, and I'd like to avoid similarly > confusing messages in the future. I think it’s because I read “after LRO” as “after LRO processing happened” which is exactly not what is happening in that case; I know logically in the code order it’s “after LRO”. If I understand the change correctly (and I think jtl summarised it quite well already as well): “In cases when LRO is disabled or LRO is not consuming the packet, try to build an mbuf chain and pass the chain to if_input() thus lowering the per-packet overheads (*). For a packet forwarding case we have seen a 12% rate improvement for small packets.” (*) would be nice to describe them at this point so people understand where 12% come from (e.g., function call overhead, locking overhead, whatever ..) because that’s the reason you are doing the change. >> Also I am pretty sure this works with ether_input but not so much >> with fddi_input, iso88025_input, and ifdead_input is probably going >> to leak as well. > > Thanks for the heads up. They all seem to use m_freem(), so they > shouldn't leak. Right. My bad. > It doesn't look like they would actually work though (except > ifdead_input of course). Well, they’d work with a bit of packet loss I guess ;-) /bz
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