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Date:      Tue, 27 Apr 1999 19:49:44 -0400 (EDT)
From:      Luoqi Chen <luoqi@watermarkgroup.com>
To:        current@freebsd.org, smp@freebsd.org
Subject:   HEADS UP! to commit SMP vmspace sharing patches
Message-ID:  <199904272349.TAA28969@lor.watermarkgroup.com>

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I'm about to commit the SMP vmspace sharing patch (the %fs approach). All
kernel modules will need to be recompiled. Recompilation is not neccessary
for user land applications including ps, libkvm and friends.

In this %fs approach, per-processor private pages are no longer mapped at
identical virtual address for each cpu, instead a new segment descriptor (%fs)
is setup to access per-cpu global variables like curproc. As a result the %fs
register needs to be saved and restored at the kernel boundary, this would
impose a small penalty (cpu model dependent) for each syscall and interrupt.
UP kernel will also be affected as efforts were made to ensure portability of
kernel modules between UP and SMP architectures.

Fast vfork is now possible for SMP and is turned on as default. We're also
able to get rid of vmspace juggling kludges in aio code, aio should now work
correctly on SMP.

-lq


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