Date: Mon, 8 May 1995 14:57:53 +1000 From: Bruce Evans <bde@zeta.org.au> To: nate@trout.sri.MT.net, rgrimes@gndrsh.aac.dev.com Cc: freebsd-hardware@FreeBSD.org, tb@emi.net Subject: Re: Intel 'ZAPPA' motherboard -details? Message-ID: <199505080457.OAA03744@godzilla.zeta.org.au>
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>> This is from a memory benchmark posted to -hackers by Bruce Evans, changed >> by L Jonas Olsson, and then changed again by Bruce Evans to correct for >> an extra store operation per loop. This is basically 4 x 32 bit memory >> read or write test per iteration of the loop written in assembler. >Any chance that we could get this benchmark into the ports tree? It is a toy. I was playing with a better one that mmaps /dev/mem to avoid cache collisions from page fragmentation, but gave up because there were too many mmap bugs. I'm more interested in measuring the cache collisions and avoiding them and in picking the best memory access order than in benchmarking. Testing memory writes safely is harder. One neat method is to write a unique pattern to pages that you own and then search for the pattern in /dev/mem. Then it is probably safe to write to overwrite when the pattern is in /dev/mem. This method also tells you the physical address of the pages that you own. I'm not sure how to find the end of physical memory. On my system, it is where accesses become very slow. Accessing nonexistent memory may cause a panic. Bruce
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