Re: [patch 05/11] syslets: core code

[Davide Libenzi <davidel@xmailserver.org>]

On Thu, 15 Feb 2007, Linus Torvalds wrote:

> I don't think the "atom" approach is bad per se. I think it could be fine 
> to have some state information in user space. It's just that I think 
> complex interfaces that people largely won't even use is a big mistake. We 
> should concentrate on usability first, and some excessive cleverness 
> really isn't a big advantage.
> 
> Being able to do a "open + stat" looks like a fine thing. But I doubt 
> you'll see a lot of other combinations.

I actually think that building chains of syscalls bring you back to a 
multithreaded solution. Why? Because suddendly the service thread become 
from servicing a syscall (with possible cachehit optimization), to 
servicing a whole session. So the number of service threads needed (locked 
down by a chain) becomes big because requests goes from being short-lived 
syscalls to long-lived chains of them. Think about the trivial web server, 
and think about a chain that does open->fstat->sendhdrs->sendfile after an 
accept. What's the difference with a multithreaded solution that does 
accept->clone and execute the above code in the new thread? Nada, NIL. 
Actually, there is a difference. The standard multithreaded function is 
easier to code in C than with the complex atoms chains. The number of 
service thread becomes suddendly proportional to the number of active 
sessions.
The more I look at this, the more I think that async_submit should submit 
simple syscalls, or an array of them (unrelated/parallel).



- Davide


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