linux-kernel - Re: [PATCH 2 of 4] Introduce i386 fibril scheduling

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Date:	Fri, 2 Feb 2007 15:37:09 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zach Brown <zach.brown@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-aio@...ck.org, Suparna Bhattacharya <suparna@...ibm.com>,
	Benjamin LaHaise <bcrl@...ck.org>
Subject: Re: [PATCH 2 of 4] Introduce i386 fibril scheduling

On Fri, 2 Feb 2007, Ingo Molnar wrote:

> in fact an app could also /trigger/ the execution of a syscall in a 
> different context - to create parallelism artificially - without any 
> blocking event. So we could do:
> 
>   cookie1 = sys_async(sys_read, params);
>   cookie2 = sys_async(sys_write, params);
> 
>   [ ... calculation loop ... ]
> 
>   wait_on_async_syscall(cookie1);
>   wait_on_async_syscall(cookie2);
> 
> or something like that. Without user-space having to create threads 
> itself, etc. So basically, we'd make kernel threads more useful, and 
> we'd make threading safer - by only letting syscalls thread.

Since I still think that the many-thousands potential async operations 
coming from network sockets are better handled with a classical event 
machanism [1], and since smooth integration of new async syscall into the 
standard POSIX infrastructure is IMO a huge win, I think we need to have a 
"bridge" to allow async completions being detectable through a pollable 
(by the mean of select/poll/epoll whatever) device.
In that way you can handle async operations with the best mechanism that 
is fit for them, and gather them in a single async scheduler.

[1] Unless you really want to have thousands of kthreads/fibrils lingering 
    on the system.

- Davide

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