Date: Mon, 27 Jul 2015 02:17:45 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: kpneal@pobox.com Cc: svn-src-all@freebsd.org Subject: Re: svn commit: r284959 - in head: . share/man/man4 share/man/man9 sys/conf sys/dev/glxsb sys/dev/hifn sys/dev/random sys/dev/rndtest sys/dev/safe sys/dev/syscons sys/dev/ubsec sys/dev/virtio/random sy... Message-ID: <20150726231745.GV44094@zxy.spb.ru> In-Reply-To: <20150726230137.GB66594@neutralgood.org> References: <FFAED695-145A-45F5-988D-B843EF5F544B@FreeBSD.org> <alpine.BSF.2.20.1507221249120.1071@desktop> <FFFB06D7-164B-40B3-AFC3-A6630BCF074E@bsdimp.com> <E20B169F-4C8A-4D11-9853-5C2EFC116450@FreeBSD.org> <F54A96A8-D9AD-409A-814F-538B6AD3CD50@yahoo.com> <20150724012519.GE78154@funkthat.com> <BC734D25-375C-4C1C-BA8A-BD91158B6A39@FreeBSD.org> <96EA33AB-7325-4DD2-83F4-B4FAF6F47CB5@yahoo.com> <20150725085209.GI43740@zxy.spb.ru> <20150726230137.GB66594@neutralgood.org>
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On Sun, Jul 26, 2015 at 07:01:37PM -0400, kpneal@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.
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