Article View: comp.sys.intel
Article #1884Re: function start address allignment
From: Rick Richardson
Date: Fri, 03 Mar 1989 15:00
Date: Fri, 03 Mar 1989 15:00
20 lines
1532 bytes
1532 bytes
In article <795@microsoft.UUCP> philba@microsoft.UUCP (Phil Barrett) writes:
>
>Actually, I believe the reason is performance. The 386 needs to have fetched
>the entire instruction before it can begin execution of it. By aligning
>the target of a control transfer, you can minimize the number of DWord fetches
>required to start execution of the instruction and thus improve the performance
>of your program.
Except that instructions can be a short as one byte, and most functions
will start off with a "pushl" which is one byte. In tests I've
run, the performance differences vary. With a cache, unaligned
is very slightly faster than aligned. Without a cache, aligned
is slighty faster than unaligned. The speed difference is less
than 1% in any case.
--
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Path: arc1-ca.pugleaf.net!utzoo!attcan!uunet!pcrat!rick From: rick@pcrat.UUCP (Rick Richardson) Newsgroups: comp.sys.intel Subject: Re: function start address allignment Keywords: word alignment Message-ID: <690@pcrat.UUCP> Date: 3 Mar 89 15:00:42 GMT References: <311@ssp2.idca.tds.philips.nl> <687@pcrat.UUCP> <795@microsoft.UUCP> Reply-To: rick@pcrat.UUCP (Rick Richardson) Organization: PC Research, Inc., Tinton Falls, NJ Lines: 20