Date: Fri, 27 Mar 2009 12:16:02 -0700 From: Chuck Swiger <cswiger@mac.com> To: Scott Long <scottl@samsco.org> Cc: Sergey Babkin <babkin@verizon.net>, freebsd-hackers@FreeBSD.org, attilio@FreeBSD.org, phk@phk.freebsd.dk, freebsd-current@FreeBSD.org, Robert Watson <rwatson@FreeBSD.org>, prashant.vaibhav@gmail.com Subject: Re: Improving the kernel/i386 timecounter performance (GSoC proposal) Message-ID: <2C3C7185-CB37-4067-B2A9-A03B5B288606@mac.com> In-Reply-To: <49CD1B3D.3030103@samsco.org> References: <11609492.9579.1238167614335.JavaMail.root@vms070.mailsrvcs.net> <49CD0405.1060704@samsco.org> <alpine.BSF.2.00.0903271821060.60642@fledge.watson.org> <49CD1B3D.3030103@samsco.org>
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Hi, Scott & all-- On Mar 27, 2009, at 11:30 AM, Scott Long wrote: > Robert Watson wrote: >> On Fri, 27 Mar 2009, Scott Long wrote: >>> I've been talking about this for years. All I need is help with >>> the VM magic to create the page on fork. I also want two pages, >>> one global for gettimeofday (and any other global data we can >>> think of) and one per-process for static data like getpid/getgid. >> FWIW, there are some variations in schemes across OS's -- one >> extreme is the Linux approach, which actually exports a mini shared >> library in ELF format on the shared page, providing implementations >> of various services (such as entering system calls), time stuff, >> etc. Less extreme are the shared pages offered on Mac OS X, etc. > > Yes, but I'd like to start somewhere, and considering that it's been > impossible in _5_ years to get the 30 minutes of Peter or JeffR or JHB > time to get the basic VM magic done, I'm keeping my expectations as > modest as possible. I'm not entirely sure how close the Mach/xnu and FreeBSD implementations of pmap_* stuff are, but the xnu code for commpage stuff is here: http://www.opensource.apple.com/darwinsource/Current/xnu-1228.9.59/osfmk/i386/pmap.c [pmap_commpage32_init(), pmap_commpage64_init()] http://www.opensource.apple.com/darwinsource/Current/xnu-1228.9.59/osfmk/i386/commpage/ [all :-)] http://www.opensource.apple.com/darwinsource/Current/xnu-1228.9.59/osfmk/i386/commpage/commpage_gettimeofday.s [but this one in particular] http://www.opensource.apple.com/darwinsource/Current/xnu-1228.9.59/osfmk/vm/vm_shared_region.c [cf "COMM PAGE" comments, vm_commpage_init()] http://www.opensource.apple.com/darwinsource/Current/xnu-1228.9.59/bsd/kern/kern_fork.c [fork_create_child(), procdup(), uses of pmap_map_sharedpage()] [ ADC login might be needed, otherwise I think rwatson has been importing xnu periodically for TrustedBSD or other work, and might be able to provide similar pointers... ] Regards, -- -Chuck
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