Re: CVS commit: src/sys

On Jun 24, 10:02pm, tlsrek.tjls.com (Thor Lancelot Simon) wrote:
-- Subject: Re: CVS commit: src/sys

| On Sun, Jun 24, 2007 at 04:10:18PM -0400, der Mouse
wrote:
| > > It seems to me (and in fact I maintain a libc
that does this) that
| > > there are a number of system calls whose result
can be known to libc
| > > without bothering to talk to the kernel.  The
obvious ones are
| > > getpid(), getppid(), and so forth but
getgroups() ought to fall into
| > > this category too after the first call, and
barring any use of
| > > certain intermediate syscalls.
| > 
| > getppid actually does not qualify, since the parent
can die, and the
| > ppid thus change to 1, without libc having a chance
to notice.
| 
| Well, this can be handled with an appropriate kevent and
some kernel magic
| -- though I would not necessarily advocate that for
NetBSD's libc.
| 
| > > This would cause problems for applications that
mixed hand-coded
| > > syscalls and libc, but I'm not so sure I care,
| > 
| > Why not?  Do you have reason to think nobody is doing
that?  (Not
| > having reason to think anybody is is not the same as
having reason to
| > think nobody is.)
| 
| I'm not sure I care because if you do things behind the C
runtime's back,
| you're in the realm of implementation-defined behavior and
_that_ is your
| own lookout.
| 
| > Furthermore, you don't mention any reason to think
that the calls that
| > can be optimized this way are used heavily enough to
make it worth the
| > bother - and potential compatability issues - of
doing so.  Do you have
| > such a reason?
| 
| Indeed, I do.  This optimization for getpid() alone yields
hundreds of
| transactions per second of improvement on the primary
benchmark for my
| application, all because of avoided context switches into
the kernel and
| back.  It also yields a measurable improvement in system
build times since
| the build framework is a fairly heavy getpid() user. 
That's valuable enough
| to me to maintain it in my libc at work; whether it is
valuable enough to
| NetBSD, I don't know.

It would be nice if someone implemented a commpage for
NetBSD and stuffed all
this info there.

christos

On Jun 24, 2007, at 7:13 PM, Christos Zoulas wrote:

> It would be nice if someone implemented a commpage for
NetBSD and  
> stuffed all
> this info there.

I have a partial implementation, though it is hardly
applicable for  
things like the pid of a process (commpage is supposed to be
stuff  
that is common across the system).

-- thorpej