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Re: FastCGI-like stuff and Forth

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Paul Rubin <no.email@nospam.invalid> wrote:
> Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>>> Yes, think of the megabyte or so of stack space allocated per thread
>>> (maybe there is a way to adjust that, but still...).
>>
>> So what?  That megabyte is only allocated in the sense that the
>> addresses are reserved.  There is no memory actually involved until
>> the page is first touched.
> 
> And on big x86 linuxes these days, the page size is 1MB(?).

Those are huge pages, and they're only used if your memory request is
a multiple of the page size.  I rather hope that huge pages aren't
used by default for thread stacks, but I guess it's not impossible.

> Even with 4k page size, that's still far more mmemory per thread
> than the few hundred or so bytes for a Forth task.

Hmmm.  I doubt very much that it makes sense for tasks to share pages,
but maybe.

>> Perhaps, but I suspect that each of those millions of threads doesn't
>> have an I/O socket of its own.
> 
> What's a socket?  It's just an integer (file descriptor) that indexes
> some table in the kernel.  Yes there are associated kernel data
> structures so the total number of open ports is limited, but it's to a
> pretty big number.  The GHC guys[1] claim to have tested with up to
> 300,000 connections, though idle.

Sure, I can beleieve that.

>> You've still got this nasty problem that you're running two
>> schedulers, one in the kernel and one in user space, fighting for
>> control.  There is an argument for moving part of the scheduler into
>> user space to facilitate very lightweight threads, I agree, but
>> complexifying the (already pretty complex) system so much frightens
>> me.
> 
> I may be missing something but I don't understand this scheduler issue.
> 
> 1) I thought Forth multitasking was basically a coroutine switch,
> i.e. it's essentially just a cleaner way to organize the control
> structure of a traditional single-threaded event loop.  So there's
> not really a scheduler fighting against another one.  Just an event
> loop with a tiny bit more overhead due to the task switch (hopefully
> less than 100 cycles, maybe just a dozen or so, compared to 1000's
> for OS thread switches).

OK, but somehow you're going to have to do load balancing between
cores.  The kernel can't split a single thread that happens to be
running a bunch of tasks, so you have to have some way of moving a
task from one thread to another.

> 2) Even if there's two schedulers, is that so bad?

If it really is the best way to do it, no.  Sometimes complexity
really is justified.  Color me skeptical.

Andrew.

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Thread

FastCGI-like stuff and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-04-03 13:28 +0000
  Re: FastCGI-like stuff and Forth Paul Rubin <no.email@nospam.invalid> - 2012-04-03 11:44 -0700
    Re: FastCGI-like stuff and Forth Bernd Paysan <bernd.paysan@gmx.de> - 2012-04-03 21:46 +0200
      Re: FastCGI-like stuff and Forth Paul Rubin <no.email@nospam.invalid> - 2012-04-03 13:25 -0700
        Re: FastCGI-like stuff and Forth Bernd Paysan <bernd.paysan@gmx.de> - 2012-04-03 22:35 +0200
          Re: FastCGI-like stuff and Forth Paul Rubin <no.email@nospam.invalid> - 2012-04-04 02:20 -0700
            Re: FastCGI-like stuff and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-04-04 05:52 -0500
              Re: FastCGI-like stuff and Forth Paul Rubin <no.email@nospam.invalid> - 2012-04-05 00:03 -0700
                Re: FastCGI-like stuff and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-04-05 03:03 -0500
                Re: FastCGI-like stuff and Forth Paul Rubin <no.email@nospam.invalid> - 2012-04-05 10:42 -0700
                Re: FastCGI-like stuff and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-04-06 06:30 -0500
                Re: FastCGI-like stuff and Forth Paul Rubin <no.email@nospam.invalid> - 2012-04-07 01:44 -0700
                Re: FastCGI-like stuff and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-04-07 19:04 -0500
                Re: FastCGI-like stuff and Forth Paul Rubin <no.email@nospam.invalid> - 2012-04-07 17:40 -0700
        Re: FastCGI-like stuff and Forth quiet_lad <gavcomedy@gmail.com> - 2012-04-05 13:37 -0700
    Re: FastCGI-like stuff and Forth Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-04-04 13:20 +0000
      Re: FastCGI-like stuff and Forth Paul Rubin <no.email@nospam.invalid> - 2012-04-04 11:20 -0700
    Re: FastCGI-like stuff and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-04-04 13:42 +0000
  Re: FastCGI-like stuff and Forth Spam@ControlQ.com - 2012-04-04 17:00 -0400
  Re: FastCGI-like stuff and Forth quiet_lad <gavcomedy@gmail.com> - 2012-04-05 13:36 -0700
  Re: FastCGI-like stuff and Forth quiet_lad <gavcomedy@gmail.com> - 2012-04-13 23:10 -0700

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