Followup to: <Pine.LNX.firstname.lastname@example.org>
By author: dean gaudet <email@example.com>
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.
> > firstname.lastname@example.org/msg13584.html">http://email@example.com/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 here's the post i originally made on the topic.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
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
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