Date: Sun, 3 Feb 2002 13:33:18 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Alfred Perlstein <bright@mu.org> Cc: Michal Mertl <mime@traveller.cz>, hackers@FreeBSD.ORG Subject: Re: stack alignment issues (was: unbelievable benchmark output) Message-ID: <20020203193318.GA6310@dan.emsphone.com> In-Reply-To: <20020203085941.N10817@elvis.mu.org> References: <Pine.BSF.4.41.0202021843210.5132-100000@prg.traveller.cz> <20020203085941.N10817@elvis.mu.org>
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In the last episode (Feb 03), Alfred Perlstein said: > * Michal Mertl <mime@traveller.cz> [020203 08:17] wrote: > > Several runs of the program take about the same time but the time > > changes wildly when the executable is called differently. > > > > The only thing which I can think of that can be causing this is > > some memory alignment issue. > > It sure looks like an alignment issue. If you print the address of > 'i' and 'j' in the attached program you can see for the fast case > they are aligned to 8 byte boundries, but when it's slow they are at > an address that is a multiple of 4 but not 8. > > Not really sure what to make of this, anyone else know how we ought > to fix this? This has actually been an issue for ages, most commonly seen with doubles. take a look at the thread at http://www.freebsd.org/cgi/getmsg.cgi?fetch=393691+0+/usr/local/www/db/text/2000/freebsd-current/20000507.freebsd-current or, easier to read the entire thread: http://groups.yahoo.com/group/freebsd-current/messages/39583?threaded=1 -- Dan Nelson dnelson@allantgroup.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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