Date: Sat, 15 Jun 2013 11:05:16 +0800 From: Julian Elischer <julian@freebsd.org> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: Ermal Lu?i <eri@freebsd.org>, freebsd-net <freebsd-net@freebsd.org> Subject: Re: [PATH] ALTQ(9) codel algorithm implementation Message-ID: <51BBD9EC.3090904@freebsd.org> In-Reply-To: <20130614100828.GA48119@onelab2.iet.unipi.it> References: <CAPBZQG0XDmybC5tzchFrcf3TZC7uJ0VcKSX-cVMJ%2BsMZUUqWVg@mail.gmail.com> <20130614095125.GQ12443@FreeBSD.org> <20130614100828.GA48119@onelab2.iet.unipi.it>
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On 6/14/13 6:08 PM, Luigi Rizzo wrote: > On Fri, Jun 14, 2013 at 01:51:25PM +0400, Gleb Smirnoff wrote: >> Ermal, > ... >> I'm afraid we can't grow mbuf packet header with 8 bytes just to satisfy >> the ALTQ codel algo, which would definitely have a limited usage among >> FreeBSD users. Thus, "enqueue_time" should go into mbuf_tags(9) not into >> mbuf packet header. in -current there are currently 2 pad bytes as I just grew it by 16 bits and wanted to get it 32 bit aligned. is there something you can do with 2 bytes to make the overhead less than a tag? tags are not as expensive as they seem however (last I checked). > not to take positions one way or the other, but getting and releasing > a tag on every packet is going to kill performance. > > If i remember well, 2-3 years ago at bsdcan there was discussion > (and mention of some pending work, jeffr maybe ?) > on providing some leading space in the mbuf so one could put there > tags (e.g. ipfw and dummynet ones) without having to allocate them. > Not sure where is this. yes we discussed this and nothing came of it but it's still a valid point of discussion. > > The other thing with codel is that it needs a fairly coarse > timer resolution (100us..1ms) to work so one might be happy > with shorter timestamps (e.g. 4 bytes) if space allows them. > > cheers > luigi > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" > >
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