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SubjectRE: SMP scalability: 8 -> 32 CPUs

Well.. The question was of Linux's SMP scalability in general, not just
running a single app.. When running multiple differnt apps your
bottlenecks are serialization in the kernel, and IO.

On Sat, 28 Nov 1998, Richard Solis wrote:

> For a good overview of the challenges associated with getting good
> performance out of multiple processors (SMPs and clusters), see "In Search
> of Clusters" by Gregory F. Pfister. I bought it a year ago when the first
> edition hit and then later got the second edition. It's a good book written
> by a guy who worked at IBM's Watson Research Facility.
>
> It turns out that neither memory or I/O is the real reason that you can't
> get good performance from multiple processors. It's the programs! Some
> problems are hard to solve in anything but a serial fashion so adding
> processors doesn't help. Some programs (like databases) access certain
> portions of data frequently, so you have collisions between the processors
> all trying to access the same data, etc. There are whole buckets of
> reasons. They basically fall into serialization, memory coherence, and
> overhead (granularity) associated with propogating updates to data shared by
> multiple processors.


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