Messages in this thread | | | From | "H. Peter Anvin" <> | Subject | Re: X15 alpha release: as fast as TUX but in user space (fwd) | Date | 29 Apr 2001 13:19:28 -0700 |
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Followup to: <Pine.LNX.4.33.0104290914260.14261-100000@twinlark.arctic.org> By author: dean gaudet <dean-list-linux-kernel@arctic.org> In newsgroup: linux.dev.kernel > > On Sun, 29 Apr 2001, Jeff Garzik wrote: > > > "H. Peter Anvin" wrote: > > > We discussed this at the Summit, not a year or two ago. x86-64 has > > > it, and it wouldn't be too bad to do in i386... just noone did. > > > > It came up long before that. I refer to the technique in a post dated > > Nov 17, even though I can't find the original. > > http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg13584.html > > > > Initiated by a post from (iirc) Dean Gaudet, we found out that > > gettimeofday was one particular system call in the Apache fast path that > > couldn't be optimized well, or moved out of the fast path. After a > > couple of suggestions for improving things, Linus chimed in with the > > magic page suggestion. > > heheh. i can't claim that i was the first ever to think of this. but > here's the post i originally made on the topic. iirc a few folks said > "security horror!"... then last year ingo and linus (and probably others) > came up with a scheme everyone was happy with. > > i was kind of solving a different problem with the code page though -- the > ability to use rdtsc on SMP boxes with processors of varying speeds and > synchronizations. >
The thing that made me say we discussed this last month was Richard's comment that it had already been implemented (which it has, by Andrea, for x86-64.) The idea of doing it for i386 has been kicked around for years, originally as a way to handle INT 0x80 vs SYSENTER vs SYSCALL, which I think is part of why it never got implemented, since handling multiple flavours of system calls apparently causes some pain in the system call entry/exit path.
The handling of a few things like gettimeofday etc. was something we observed could be added on top at that time, but was largely considered secondary.
-hpa
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