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    SubjectRe: Voyager subarchitecture for 2.5.46
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    On Sun, 2002-11-10 at 11:46, Vojtech Pavlik wrote:
    > On Sun, Nov 10, 2002 at 10:59:55AM -0800, Linus Torvalds wrote:
    > > On Sun, 10 Nov 2002, Pavel Machek wrote:
    > > > Unfortunately, this means "bye bye vsyscalls for gettimeofday".
    > >
    > > Not necessarily. All of the fastpatch and the checking can be done by the
    > > vsyscall, and if the vsyscall notices that there is a backwards jump in
    > > time it just gives up and does a real system call. The vsyscall does need
    > > to figure out the CPU it's running on somehow, but that should be solvable
    > > - indexing through the thread ID or something.
    >
    > I'm planning to store the CPU number in the highest bits of the TSC ...

    I could be wrong, but we had considered this earlier, and found that
    there isn't a way to set the high bits of the TSC, you can only clear
    them.


    > > The system call overhead tends to scale up very well with CPU speed (the
    > > one esception being the P4 which just has some internal problems with "int
    > > 0x80" and slowed down compared to a PIII).
    > >
    > > So I would just suggest not spending a lot of effort on it, considering
    > > the problems it already has.
    >
    > Agreed. The only problem left I see is the need to have an interrupt of
    > every CPU from time to time to update the per-cpu time values, and to
    > synchronize those to the 'global timer interrupt' somehow.

    Yes, this would be needed for per-cpu tsc.

    thanks
    -john


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