Date: Fri, 04 Mar 2005 11:38:31 -0700 From: Scott Long <scottl@samsco.org> To: David Schultz <das@FreeBSD.org> Cc: John Baldwin <jhb@FreeBSD.org> Subject: Re: cvs commit: src/sys/kern kern_sig.c Message-ID: <4228AB27.3020204@samsco.org> In-Reply-To: <20050304182629.GA39457@VARK.MIT.EDU> References: <200503021343.j22DhpQ3075008@repoman.freebsd.org> <200503020915.28512.jhb@FreeBSD.org> <4226446B.7020406@freebsd.org> <61ac46c154aa515a692308440dd1141d@FreeBSD.org> <422710DD.1070203@freebsd.org> <422719E0.10703@samsco.org> <42279B6D.1000005@freebsd.org> <20050304182629.GA39457@VARK.MIT.EDU>
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David Schultz wrote: > On Fri, Mar 04, 2005, David Xu wrote: > >>Scott Long wrote: >> >> >>>David Xu wrote: >>> >>> >>>>John Baldwin wrote: >>>> >>>> >>>>>Note that swapping out the stack is the default behavior in 4.x, so >>>>>I actually think that the million lines of kernel code are indeed >>>>>safe, only sigwait() is broken and should be fixed. :) >>>>> >>>> >>>>Many 4.x programming skill can not be applied to FreeBSD current, >>>>they are so different, most of code in kern/ seems be completely >>>>rewritten. :=) >>>> >>>>David Xu >>>> >>> >>>I think you're making a much bigger deal out of this than it needs to >>>be. Swapping the kernel stacks is important on real production systems. >>>FreeBSD has always been much better at handling low-memory situations >>>that most other OSes, and it's one of the things that has kept it >>>relevant in the server area. A few 16K chunks might not seem like a lot >>>on a desktop system, but when you're talking about a server with >>>hundreds of ithreads and hundreds of user processes, it matters a quite >>>a bit. Also, there is talk about increasing the default kstack size due >>>to all of the extra inlining that the compiler does with the -O2 option >>>and the large recursion problems in the softdep code. If we do this, >>>then being able to swap them out gets even more important. >>> >> >>I think your system is just a point that adding another 10M bytes memory > > [...] > > I suspect that the performance difference is not as great as some > people think, but the *real* question in my mind is: > > Is there actually more than one instance of this bug? > > In 4.X, it's pretty clear that we got things right. But I haven't > had time to follow KSE and other large projects since then to know > what developers thought the rules were when they wrote the code. > If there are problems of this nature all over the place, then > eliminating kstack swapping would be an easy way to bring the > reliability of 5.X closer to where we were with 4.X. But if there > is only one bug, then it would be disingenuous to use it as an > excuse to kill a feature that has worked since day one. That's close to my position too. I think it would be useful to investigate adding diagnostics to catch the unknown cases instead of just letting them turn into mystery panics. Scotthome | help
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