Re: DragonflyBSD fast syscall support and x86 improvements

[David Xu <davidxu@xxxxxxxxxxx>]

Attilio Rao wrote:
. ..
> Once that we have choicen a method in order to apply changes,  the
> first thing I would like to add (BTW, I don't know if it exists
> alredy) is sysenter/sysexit support replacing interrupt 0x80 (I have
> an item in the FreeBSD list for volounteers about it, since I think I
> would like to add it there too) and possibly evaluating the usage of
> FPU/MMX/XMM registers in order to gather syscalls parameters.
> Feedbacks about it are very appreciated too. I have other ongoing
> projects we can discuss later, but they are very architecture
> dependant so, since maybe they can fit in FreeBSD, they cannot in
> DragonflyBSD.
>
> Thanks for your time,
> Attilio

I have a complete patch for FreeBSD to support sysenter/sysexit,
in fact, it is running on my machine for months, but I must say
it is useless, I saw no performance improvement in real world,
yes, in benchmark world, you can measure the improvement by doing
getuid() syscall, and you found it is a lot faster, but in
real world, application is more complex, and doing heavy work
more than this simple syscall, so the micro improvment is
absorbed by heavy syscall path, result is you won't see
any improvement in real world.

You still can access the patch here:

http://people.freebsd.org/~davidxu/sysenter


David Xu