x86 hardware and transputers (Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3)

From: Oleg Verych
Date: Thu Feb 22 2007 - 14:43:30 EST

> From: "Michael K. Edwards"
> Newsgroups: gmane.linux.kernel
> Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3
> Date: Thu, 22 Feb 2007 00:59:10 -0800

[striping cc list]

> On 2/21/07, Ingo Molnar <mingo@xxxxxxx> wrote:
>> > [...] As for threadlets, making them kernel threads is not such a good
>> > design feature, O(1) scheduler or not. You take the full hit of
>> > kernel task creation, on the spot, for every threadlet that blocks.
>> > [...]
>> this is very much not how they work. Threadlets share the same basic
>> infrastructure with syslets and they do /not/ take a 'full hit of kernel
>> thread creation' when they block. Please read the announcements, past
>> discussions on lkml and the code about how it works.
> Yes, I will go back and read the code for myself. This will take me
> some time because I have only a hand-waving level of knowledge about
> task_structs and pt_regs, and have largely avoided the dark corners of
> the x86 architecture.

This architecture was brought to us by windows on our screens. And it
took years (a decade?) for them to use all hardware features:

(IA-32, i386) --> (MS Windows NT,9X)

Yet you must still do much system programming to use that features.


> But I think my point still stands: allowing code inside threadlets to
> use the usual C library wrappers around the usual synchronous syscalls
> is going to mean that the threadlet context is fairly heavyweight, both
> in memory and CPU/MMU state. This means that you can't pull it cheaply
> over to whatever CPU core happened to process the device I/O that
> delivered the data it wanted.
> Oh, and while I haven't written a kernel or an RDBMS, I have written
> some fairly serious non-blocking I/O code (without resorting to
> threads; one socket and thousands of independent userspace state
> machines) and rewritten the plumbing of two fairly heavy-duty network
> operations frameworks, one of them attached to a horrifically complex
> GUI. And briefly, long ago, I made Transputers dance with Occam and
> galaxies spin with PVM.

transputers were (AFAIK) completely orthogonal to any today's x86 CPU
architecture -- hardware parallelism, special programming language and
technique to match this hardware. And they were chosen to work on Mars in
mid-90th, while crowd wanted more stupid windows on cheap CPUs.

> This gives me exactly zero credentials here, of course, but may suggest
> to you that when I say something that seems naive, it's more likely
> that I got the Linux-specific lingo wrong. That, or I'm _actively_
> stupid. :-)

Thus, i think, you are thinking mostly on hardware level, while it's
longstanding software problem, i.e. to use x86 (:.

#oo'L O
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