Article View: comp.arch
Article #11403Re: DEC Alpha architecture issues
From: John F Carr
Date: Sun, 22 Nov 1992 16:57
Date: Sun, 22 Nov 1992 16:57
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1368 bytes
In article <By0xy0.FsA.2@cs.cmu.edu>
lindsay+@cs.cmu.edu (Donald Lindsay) writes:
>Also, PALcode can be entered from user state - you don't need to do a
>system call, with its heavy-duty state-change overheads.
A system call does not need to be slow. On an RS/6000, a system call can be
as fast as 2 cycles. If there is a slow instruction like a multiply or
divide executing the system call may overlap it and appear to take 0 cycles.
The current Alpha implementation takes more cycles than the RS/6000 to
switch modes, but that isn't an architectural issue: the 21064 pipeline is
longer.
--
John Carr (jfc@athena.mit.edu)
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Path: arc1-ca.pugleaf.net!sparky!uunet!kithrup!hoptoad!pacbell.com!iggy.GW.Vitalink.COM!cs.widener.edu!eff!sol.ctr.columbia.edu!zaphod.mps.ohio-state.edu!cs.utexas.edu!sun-barr!olivea!charnel!sifon!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!bloom-picayune.mit.edu!athena.mit.edu!jfc From: jfc@athena.mit.edu (John F Carr) Newsgroups: comp.arch Subject: Re: DEC Alpha architecture issues Message-ID: <1992Nov22.165752.26572@athena.mit.edu> Date: 22 Nov 92 16:57:52 GMT References: <1992Nov18.210416.27212@nntpd.lkg.dec.com> <lgnfc3INNqnt@spim.mti.sgi.com> <By0xy0.FsA.2@cs.cmu.edu> Sender: news@athena.mit.edu (News system) Organization: Massachusetts Institute of Technology Lines: 16 Nntp-Posting-Host: achates.mit.edu