Date: Sat, 29 Oct 2005 18:37:13 +1000 From: Peter Jeremy <PeterJeremy@optushome.com.au> To: Maxim.Sobolev@portaone.com Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, current@freebsd.org Subject: Re: Timers and timing, was: MySQL Performance 6.0rc1 Message-ID: <20051029083713.GX39882@cirb503493.alcatel.com.au> In-Reply-To: <436324C6.5040107@portaone.com> References: <37497.1130570011@critter.freebsd.dk> <436324C6.5040107@portaone.com>
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On Sat, 2005-Oct-29 00:29:10 -0700, Maxim Sobolev wrote: >Poul-Henning Kamp wrote: >>In message <4362BA38.1090603@portaone.com>, Maxim Sobolev writes: >>>You can solve most of those issues by exporting from kernel to userland >>>not only page(s) with actual data, but also page(s) with code to handle >>>that data. Then you can turn syscalls implementation in libc into plain >>>function calls to addresses in that code page(s). This approach can >>>potentially have other interesting applications, for example it will be >>>possible to use processor-specific syscalls instructions without >>>recompiling userland, move some of the ABI code into userland (i.e. >>>freebsd32 layer on amd64) etc. The data I understand - we document a struct that defines the page contents, I'm less sure about the code. The concept is appealing but some more detail would be nice. >>I'm not sure I see much difference between a shared library and this >>solution, but I'm equally sure we'd love to se a prototype before >>we judge it :-) > >Difference is that you won't have additional problems with userland and >kernel versions mismatch and don't need any additional complexity >associated with versioning/fallback logic. I'm not sure I understand how you'll achieve this. How would a userland application locate the appropriate entry points? If the exported code looks like a automagically-mapped shared library, we'd need to embed the ELF symbol table in the kernel as well. How does an application compiled for (eg) FreeBSD-6 handle the code page exported by a FreeBSD-7 kernel? Other options would seem to be: - hard-wire the entry-points into the application or libc (which will basically destroy backward/forward compatibility) - Use explicit branch tables (ala Amiga shared libraries) - there's no infrastructure to support this in FreeBSD. -- Peter Jeremy
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