Dmitry
The CPU cycles is only at most half of the story with the other half
being the memory sub-system BW.
So the validity of your observation depends on the BW we're talking
about, i.e. if the client is using a fraction of 10Gbps for RDMA (or
DDP, e.g. iSCSI DDP), yes then that fraction amounts to a fraction of
the memory sub-system total BW so we don't much care about the extra
copy.
The situation is different if the client wants something close to 10Gbps
(already have such client applications), because today 10Gbps is still a
big chunk of the overall memory BW so you really care about eliminating
that copy via DDP.
'Asgeir
> -----Original Message-----
> From: netdev-bounce@xxxxxxxxxxx [mailto:netdev-bounce@xxxxxxxxxxx] On
> Behalf Of Dmitry Yusupov
> Sent: Saturday, April 02, 2005 10:09 AM
> To: open-iscsi@xxxxxxxxxxxxxxxx
> Cc: David S. Miller; mpm@xxxxxxxxxxx; andrea@xxxxxxx;
> michaelc@xxxxxxxxxxx; James.Bottomley@xxxxxxxxxxxxxxxxxxxxx;
ksummit-2005-
> discuss@xxxxxxxxx; netdev@xxxxxxxxxxx
> Subject: Re: [Ksummit-2005-discuss] Summary of 2005 Kernel Summit
> ProposedTopics
>
> On Mon, 2005-03-28 at 17:32 -0500, Benjamin LaHaise wrote:
> > On Mon, Mar 28, 2005 at 12:48:56PM -0800, Dmitry Yusupov wrote:
> > > If you have plans to start new project such as SoftRDMA than yes.
lets
> > > discuss it since set of problems will be similar to what we've got
> with
> > > software iSCSI Initiators.
> >
> > I'm somewhat interested in seeing a SoftRDMA project get off the
ground.
> > At least the NatSemi 83820 gige MAC is able to provide early-rx
> interrupts
> > that allow one to get an rx interrupt before the full payload has
> arrived
> > making it possible to write out a new rx descriptor to place the
payload
> > wherever it is ultimately desired. It would be fun to work on if
not
> the
> > most performant RDMA implementation.
>
> I see a lot of skepticism around early-rx interrupt schema. It might
> work for gige, but i'm not sure if it will fit into 10g.
>
> What RDMA gives us is zero-copy on receive and new networking api
which
> has a potential to be HW accelerated. SoftRDMA will never avoid
copying
> on receive. But benefit for SoftRDMA would be its availability on
client
> sides. It is free and it could be easily deployed. Soon Intel & Co
will
> give us 2,4,8... multi-core CPUs for around 200$ :), So, who cares if
> one of those cores will do receive side copying?
>
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