* Poul-Henning Kamp <[EMAIL PROTECTED]> [000320 11:45] wrote:
> In message <[EMAIL PROTECTED]>, Alfred Perlstein writes:
>
> >Keeping the currect cluster code is a bad idea, if the drivers were
> >taught how to traverse the linked list in the buf struct rather
> >than just notice "a big buffer" we could avoid a lot of page
> >twiddling and also allow for massive IO clustering ( > 64k )
>
> Before we redesign the clustering, I would like to know if we
> actually have any recent benchmarks which prove that clustering
> is overall beneficial ?
Yes it is really benificial.
I'm not talking about a redesign of the clustering code as much as
making the drivers that take a callback from it actually traverse
the 'union cluster_info' rather than relying on the system to fake
the pages being contiguous via remapping.
There's nothing wrong with the clustering algorithms, it's just the
steps it has to take to work with the drivers.
>
> I would think that track-caches and intelligent drives would gain
> much if not more of what clustering was designed to do gain.
>
> I seem to remember Bruce saying that clustering could even hurt ?
Yes because of the gyrations it needs to go through to maintain backward
compatibility for devices that want to see "one big buffer" rather than
simply follow a linked list of io operations.
Not true, at least for 'devices' like NFS where large IO ops issued
save milliseconds in overhead. Unless each device was to re-buffer
IO (which is silly) or scan the vp passed to it (violating the
adstraction and being really scary like my flopped super-commit
stuff for NFS) it would make NFS performance even worse for doing
commits.
Without clustering you'd have to issue a commit RPC for each 8k block
With the current clustering you have to issue a commit for each 64k
block
With an unbounded linked list, well there is only the limit that the
filesystem asks for.
--
-Alfred Perlstein - [[EMAIL PROTECTED]|[EMAIL PROTECTED]]
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