Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!ucsd!ucbvax!decwrl!pyramid!prls!mips!mash
From: mash@mips.COM (John Mashey)
Newsgroups: comp.unix.wizards
Subject: Re: Vax 11/780 performance vs Sun 4/280 performance
Message-ID: <2298@winchester.mips.COM>
Date: 5 Jun 88 16:41:10 GMT
References: <14968@brl-adm.ARPA> <601@modular.UUCP> <7331@swan.ulowell.edu> <2282@rpp386.UUCP> <3859@lynx.UUCP>
Reply-To: mash@winchester.UUCP (John Mashey)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 21

In article <3859@lynx.UUCP> m5@lynx.UUCP (Mike McNally) writes:
...
>As a somewhat related side question, what does the Sun 4/SPARC MMU look
>like?  Are lookaside buffer reloads done in software like on the MIPS
>R[23]000?  (Is that really true about the R[23]000 anyhow?)

The Sun-4 MMU, like earlier Suns, doesn't use a TLB, but has SRAMs
for memory maps (16 contexts' worth, compared to 8 in Sun-3/200, for
example).

The R[23]000 indeed do TLB-miss refill handling in software;
this is not unusual in RISC machines: HP Precision and AMD 29K (at least)
do this also.  The overall cost if typically 1% or less of CPU time,
which is fairly competitive with hardware refill, especially since one
of the larger costs on faster machines is the accumulated cache-miss penalty
for fetching PTEs from memory.
-- 
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