Re: Global page into user processes (was: Re: Patch to cache TLS in %fp7 to avoid _lwp_getprivate syscalls)

[David Holland <dholland-current%netbsd.org@localhost>]

On Wed, Jan 18, 2012 at 01:02:22AM -0500, Matthew Mondor wrote:
 > After reading the patch and seeing the solution about mapping a global
 > page into user processes, it reminds me that a possible solution to
 > have faster time query functions (such as gettimeofday(2)) would be to
 > also have a special page+structure shared and mapped readonly+noexec in
 > every process, such that some syscalls may be replaced by libc functions
 > that access that structure, which the kernel would update.  At libc
 > initialization, a syscall (or sysctl, ELF trick or other solution) could
 > be used such that the pointer to that structure is known...
 > 
 > Since that doesn't already exist but appears at first glance rather
 > simple to implement, is there a particular reason that makes this
 > undesirable?

this has been proposed before and (AFAICR) nobody thought it was a
horrible idea, but nobody's gotten around to doing it either. go for
it....

-- 
David A. Holland
dholland%netbsd.org@localhost