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SubjectRe: 2.2.18Pre Lan Performance Rocks!


"Jeff V. Merkey" wrote:
>
> Alan Cox wrote:
> >
> > > Why not solve the problem at the source and completely redesign the
> > > network stack? Get rid of the old sk_buff & co! Rip the whole network
> > > layer out! Redesign it and give the user a possibility of Zero-Copy
> > > networking!
> >
> > For one because you don't need to do that to get zero copy networking for
> > most real world cases. Tux already implements the neccessary infrastructure
> > for these.
>
> The code in the networking layer is fine, in fact, it's absolutely
> great. This is not
> the problem. The problem are all the clocks wasted reloading TLBs and
> the background
> memory activitiy caused by Linux's heavy dependence in Intel's
> protection hardware model.
>
> Step 1 is to load the entire OS at ring 0 with protection completely
> disabled system wide,
> put in the kernel optimizations for AGI and context switch locking, and
> stub the top half of Linus's scheduler. The global memory structures in
> his kernel may or may not hurt performance, depending on how they are
> accessed by multiple processors. I will need to start profiling with a
> ring 0 port first and determine frequency of access that's hardware
> measured.
>
> The next step would be to start peeling off different subsystems and
> re-parallelizing them
> on the merged kernel. There's an awful lot of areas in Linus' that are
> going to be a
> problem, but I'll work through them one at a time. When I first
> parallelized NetWare, I wrote
> an independent SMP kernel then loaded the entire NetWare 4.1 image as a
> single process. The next step was to start peeling off layers from
> NetWare and plugging them in one by one and parallelizing them. I am
> using the same approach here. When I was finished, I had peeled NetWare
> like a banana and completely reintegrated it on a new kernel. This
> approach works because it allows you to stage each layer.
>
> The next step will be to modify the loader to allow the existing
> protection scheme to exist in true user space. WRD's will hold off CR3
> switching so long as I/O is coming in or out of the box. I anticipate
> this will take until March of next year to get right.
>
> Jeff
>


One other point. You guys can try as hard as you can to hack around
this problem, but it will never scale like NetWare unless a
fundamentally different approach is adopted. I've built this before,
and what we are doing is building in all the Linux functionality with
the identical code -- basically a Linux NetWare -- into a NetWare
framework. All the protection can still be there, it just needs to be
restructured with some LAN based design assumptions. I think the
industry will be pleased with the result. I do not believe any of the
proposed hacks will get there unless this different approach is
investigated.

Jeff




> packets via a WTD scheduler,
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