Assembly Syscall Question

[Terry Lambert]

Matthew Dillon wrote:
>     I think the ultimate performance solution is to have some explicitly
>     shared memory between kerneland and userland and store the arguments,
>     error code, and return value there.  Being a fairly small package of
>     memory multi-threading would not be an issue as each thread would have
>     its own slot.

You need 8K for this, minimally: 4K that's RO user/RW kernel and
4K that's RW user/RW kernel.  You can use it for things like zero
system call getpid/getuid/etc..

It's also worth a page doubly mapped, with the second mapping with
the PG_G bit set on it (to make it RO visible to user space at the
sampe place in all programs) to hold the timecounter information;
the current timecounter implementation, with a scad of structures,
is both wasteful and unnecessary, given that pointer assigns are
atomic, so you can implement with only two, which only take a small
part of the page.  Doing this, you can use a pointer reference and
a structure assign, and a compare-pointer-afterwards to make a zero
system call gettimeofday() and other calls (consider the benefits
to Apache, SQID, and other programs that have hard "logging with
timestamp" requirements).

I've also been toying with the idea of putting environp ** in a COW
page, and dealing with changes as a "fixup" operation in the fault
handler (really, environp needs to die, to make way for logical name
tables; it persists because POSIX and SuS demand that it persist).

So, Matt... how does the modified message based system call
interface fare in a before-and-after with "lmbench"?  8-) 8-).

-- Terry