> > The costs depend on the particular method Pth uses for the context
> > implementation, of course. But all available methods Pth uses are very
> > cheap, because they are user-space only methods. Keep also in mind that
> > because Pth is a non-preemtive threading implementation, the context
> > switching is only performed if really required by the I/O.
> There is no reason a user-space context switch should be
> any faster than a
> kernel-space context switch unless the user-space context switch saves a
> kernel call. Measurements under Linux (at least) bear this out.
[snip]
I should point out that you didn't actually say that user-space context
switches are always faster than kernel context switches (which is false).
What you did say is that user-space only context swithces are generally
quite fast (which is true).
So I'm not dsiagreeing with you. I'm just pointing out that there's usally
kernel overhead associated with these user-space context switches,
especially if they're associated with I/O blocking.
DS
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