Re: TSS and context switch

hjl@lucon.org
Fri, 15 Jan 1999 11:29:22 -0600


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Subject: Re: TSS and context switch
From: dillon@apollo.backplane.com (Matthew Dillon)
Date: 1999/01/15
Newsgroups: muc.lists.freebsd.hackers,mpc.lists.freebsd.hackers
:"Ron G. Minnich" <rminnich@Sarnoff.COM> writes:
:
:> I'm assuming you measured all this and determined that TSS was faster?
:>
:> Ron
:Let's make it simpler for him. Why don't you just let him look
:in the architecture manual for the 386/486/586 and PII and see
:how many cycles the load and save takes compared to what is done
:in practice.

The Intel TSS stuff is *extremely* *slow* compared to doing it
with discrete instructions, especially since many of the major
supervisory registers do not change.

There are a number of intel instructions which were designed to
run fast on a 486, which turn out to be dogs on higher-end cpu's.
For example, the ENTER instruction is considerably slower then
doing the frame pointer / stack pointer manipulation manually.

There are many others.

-Matt

Matthew Dillon
<dillon@backplane.com>

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