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SubjectRe: smp overhead, and rwlocks considered harmful
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On Sun, 2003-03-23 at 12:33, Michael Vergoz wrote:
> Hi Andrew,
>
> I would like to noticed to you that the SMP capacity can't be used on one process under Linux.
>
> when you run 'time dd if=/dev/zero of=foo bs=1 count=1M', the capacity of 1 processor will
> use since your command sets is executed in ONE process.

Your dd is benchmarking the lock operations in the C library I suspect.
The kernel will happily use both processors and a given syscall can
evne start on one cpu and complete on another, or have the IRQ tasks
executed on its behalf on another CPU.

There are *good* reasons btw for avoiding splitting stuff too far, the
cost of copying data between processor caches is very high.

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