Date: Sat, 10 Aug 2002 10:56:44 -0400 From: Bosko Milekic <bmilekic@unixdaemons.com> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: ken@FreeBSD.ORG, freebsd-net@FreeBSD.ORG Subject: Re: Jumbo Clusters in mb_alloc Message-ID: <20020810105644.A92823@unixdaemons.com> In-Reply-To: <15700.13575.470677.723138@grasshopper.cs.duke.edu>; from gallatin@cs.duke.edu on Fri, Aug 09, 2002 at 05:32:55PM -0400 References: <20020809151627.A88180@unixdaemons.com> <15700.9669.885383.727182@grasshopper.cs.duke.edu> <20020809164136.A88798@unixdaemons.com> <15700.13575.470677.723138@grasshopper.cs.duke.edu>
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On Fri, Aug 09, 2002 at 05:32:55PM -0400, Andrew Gallatin wrote:
[...]
> bus_dmamap_load_mbuf(sc->sc_dmat, dmamap, m0,
> BUS_DMA_WRITE|BUS_DMA_NOWAIT) != 0) {
> MGETHDR(m, M_DONTWAIT, MT_DATA);
>
> Methinks its high time we adopted this interface.
It's really funny that I remember implementing this for Mark Murray
quite a while ago for crypto stuff he was then working on, and now
just recently Sam Leffler - who's doing all the cool crypto work these
days - also mentionned he's already ported it and using it - and on
top of it, you've ported it and are using it! - yet, we still haven't
really merged our efforts. :-) I agree that we absolutely need this
interface and it should know how to deal with both a chain of mbufs
with regular clusters as well as a chain/or single mbuf with [a] jumbo
cluster[s].
> > What about the send case, though? How do you want to determine
>
> The send case opens a huge can-of-worms. Lets say that somebody is
> forwarding between myrinet & GigE using FreeBSD, with myri0 on the
> myrinet network, and em0 on GigE. Let's assume that myri0 is using
> jumbo buffers, but em0 isn't jumbo aware & cannot accept them & the
> forwarded packets end up as garbage.
>
> Perhaps we need to add an IFCAP_JUMBOAWARE flag and somwhere
> (IF_DEQUE?) add a KASSERT to catch situaions like this.
> Or even.. ick, add code to copy to a normal mbuf chain.
Wow, I had not even thought of that, actually. My concern was how we
were going to deal with things like sendto() which currently allocate
regular clusters. In some cases, it would be advantageous for them to
allocate the jumbo clusters if the outgoing interface supports them.
Anyway, the forwarding example you bring up is at least equally
interesting. I suppose that for these [hopefully rare] cases we could
perform a copy. Although, I have a question: is it possible to
somehow "peek" at the data to see if it is a packet that we're
forwarding to an interface that isn't IFCAP_JUMBOAWARE and, if so,
just DMA into a chain of mbufs with regular clusters?
> Drew
Cheers,
--
Bosko Milekic * bmilekic@unixdaemons.com * bmilekic@FreeBSD.org
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