Re: [parisc-linux] Generic light-weight syscall.

[Randolph Chung <tausq@debian.org>]

> I'd say we should keep doing stuff on our existing gateway page until we
> exhaust it.  We've got plenty of space -- 248 instruction slots left before
> 0xE0, and a lot of space left after the syscall handler.
> 
> On a related subject, fast gettimeofday is always a popular idea.  I'm not

Why not add a flag to syscall() which indicates whether this is a "fast"
syscall or a "slow" syscall, and based on this, decide whether to do all
the register spilling, etc when entering the kernel?  Then we can
implement the atomic ops as additional "syscalls"....

I would think that there is at least some amount of logic that needs to
be there everytime you enter/exit the kernel, irregardless of whether
you are doing a "fast syscall" (i.e. no need to save the processor
state, etc) or a regular one... i would hope we don't need to have two
copies of that logic.

Carlos had some concerns that this means fast syscalls (or regular ones
perhaps) will always incur a mispredicted branch and/or extra stack
manipulations that may not be needed..... but i'm not yet convinced that
there is enough overhead to make this a problem. what do others think?

thanks,
randolph
-- 
Randolph Chung
Debian GNU/Linux Developer, hppa/ia64 ports
http://www.tausq.org/