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diff --git a/open_issues/performance.mdwn b/open_issues/performance.mdwn index ec14fa52..ae05e128 100644 --- a/open_issues/performance.mdwn +++ b/open_issues/performance.mdwn @@ -81,3 +81,137 @@ call|/glibc/fork]]'s case. gnumach and the hurd) just wake every thread waiting for an event when the event occurs (there are a few exceptions, but not many) <antrik> ouch + + +## [[!message-id "20121202101508.GA30541@mail.sceen.net"]] + + +## IRC, freenode, #hurd, 2012-12-04 + + <damo22> why do some people think hurd is slow? i find it works well even + under heavy load inside a virtual machine + <braunr> damo22: the virtual machine actually assists the hurd a lot :p + <braunr> but even with that, the hurd is a slow system + <damo22> i would have thought it would have the potential to be very fast, + considering the model of the kernel + <braunr> the design implies by definition more overhead, but the true cause + is more than 15 years without optimization on the core components + <braunr> how so ? + <damo22> since there are less layers of code between the hardware bare + metal and the application that users run + <braunr> how so ? :) + <braunr> it's the contrary actually + <damo22> VFS -> IPC -> scheduler -> device drivers -> hardware + <damo22> that is monolithic + <braunr> well, it's not really meaningful + <braunr> and i'd say the same applies for a microkernel system + <damo22> if the application can talk directly to hardware through the + kernel its almost like plugging directly into the hardware + <braunr> you never talk directly to hardware + <braunr> you talk to servers instead of the kernel + <damo22> ah + <braunr> consider monolithic kernel systems like systems with one big + server + <braunr> the kernel + <braunr> whereas a multiserver system is a kernel and many servers + <braunr> you still need the VFS to identify your service (and thus your + server) + <braunr> you need much more IPC, since system calls are "replaced" with RPC + <braunr> the scheduler is basically the same + <damo22> okay + <braunr> device drivers are similar too, except they run in thread context + (which is usually a bit heavier) + <damo22> but you can do cool things like report when an interrupt line is + blocked + <braunr> and there are many context switches between all that + <braunr> you can do all that in a monolithic kernel too, and faster + <braunr> but it's far more elegant, and (when well done) easy to do on a + microkernel based system + <damo22> yes + <damo22> i like elegant, makes coding easier if you know the basics + <braunr> there are only two major differences between a monolilthic kernel + and a multiserver microkernel system + * damo22 listens + <braunr> 1/ independence of location (your resources could be anywhere) + <braunr> 2/ separation of address spaces (your servers have their own + addresses) + <damo22> wow + <braunr> these both imply additional layers of indirection, making the + system as a whole slower + <damo22> but it would be far more secure though i suspect + <braunr> yes + <braunr> and reliable + <braunr> that's why systems like qnx were usually adopted for critical + tasks + <damo22> security and reliability are very important, i would switch to the + hurd if it supported all the hardware i use + <braunr> so would i :) + <braunr> but performance matters too + <damo22> not to me + <braunr> it should :p + <braunr> it really does matter a lot in practice + <damo22> i mean, a 2x slowdown compared to linux would not affect me + <damo22> if it had all the benefits we mentioned above + <braunr> but the hurd is really slow for other reasons than its additional + layers of indrection unfortunately + <damo22> is it because of lack of optimisation in the core code? + <braunr> we're working on these issues, but it's not easy and takes a lot + of time :p + <damo22> like you said + <braunr> yes + <braunr> and also because of some fundamental design choices related to the + microkernel back in the 80s + <damo22> what about the darwin system + <damo22> it uses a mach kernel? + <braunr> yes + <damo22> what is stopping someone taking the MIT code from darwin and + creating a monster free OS + <braunr> what for ? + <damo22> because it already has hardware support + <damo22> and a mach kernel + <braunr> in kernel drivers ? + <damo22> it has kernel extensions + <damo22> you can do things like kextload module + <braunr> first, being a mach kernel doesn't make it compatible or even + easily usable with the hurd, the interfaces have evolved independantly + <braunr> and second, we really do want more stuff out of the kernel + <braunr> drivers in particular + <damo22> may i ask why you are very keen to have drivers out of kernel? + <braunr> for the same reason we want other system services out of the + kernel + <braunr> security, reliability, etc.. + <braunr> ease of debugging + <braunr> the ability to restart drivers separately, without restarting the + kernel + <damo22> i see + + +# IRC, freenode, #hurd, 2012-09-13 + +{{$news/2011-q2#phoronix-3}}. + + <braunr> the phoronix benchmarks don't actually test the operating system + .. + <hroi_> braunr: well, at least it tests its ability to run programs for + those particular tasks + <braunr> exactly, it tests how programs that don't make much use of the + operating system run + <braunr> well yes, we can run programs :) + <pinotree> those are just cpu-taking tasks + <hroi_> ok + <pinotree> if you do a benchmark with also i/o, you can see how it is + (quite) slower on hurd + <hroi_> perhaps they should have run 10 of those programs in parallel, that + would test the kernel multitasking I suppose + <braunr> not even I/O, simply system calls + <braunr> no, multitasking is ok on the hurd + <braunr> and it's very similar to what is done on other systems, which + hasn't changed much for a long time + <braunr> (except for multiprocessor) + <braunr> true OS benchmarks measure system calls + <hroi_> ok, so Im sensing the view that the actual OS kernel architecture + dont really make that much difference, good software does + <braunr> not at all + <braunr> i'm only saying that the phoronix benchmark results are useless + <braunr> because they didn't measure the right thing + <hroi_> ok |