On Sun, Jul 26, 2015 at 07:01:37PM -0400, kpn...@pobox.com wrote: > On Sat, Jul 25, 2015 at 11:52:09AM +0300, Slawa Olhovchenkov wrote: > > On Fri, Jul 24, 2015 at 11:06:59PM -0600, Scott Long via svn-src-all wrote: > > > > > > I'm working on a premise of "tools, not policy". I'd like there to be > > > > enough harvesting points for the box owner to get the warm fuzzies. > > > > If they choose to use less, fine by me. > > > > > > > > > > Sure, and that's not an unreasonable goal, but the devil is in the > > > details. > > > It's an unfortunate fact of modern CPU architecture that even something > > > as simple and innocent as a run-time control that checks a variable can > > > cause significant performance problems, thanks to the penalty of cache > > > misses and bus contention between lots of CPU cores. Maybe these > > > "extended" collection points should be controlled with a compile-time > > > option? > > > > I am hate compile-time option, may be time to introduction some JIT in > > project? As global feature. > > I agree with your dislike of compile-time options, and this is especially > true in the OS itself. > > However, a JIT is rather large, and is a rather large effort as well. A > JIT in the kernel would scare the heck out of me because ensuring it didn't > have exploitable security issues would be a lost cause. You could have the > kernel call out to a userland JIT that created (re)loadable modules, but > you'd need to have the source either in kernel, or you'd need to be certain > that all the relevant source was installed. > > Simpler JITs could be written, but that is a large amount of effort for > generated code that wouldn't be as good as the system compiler's code. > > Heck, I ported a 31-bit (yes, thirty-one) JIT for MVS to 64-bit z/OS (modern > MVS), working full time, and it still took me two and a half years to > finish it.
For some purpose may be enough some limited, very specific JIT. For example, BPF have JIT as option. 'JIT for options' may be working just as in-place patching (replace call by nops), as example. _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
