Date: Tue, 25 Apr 2006 10:46:37 -0400 From: Chuck Swiger <cswiger@mac.com> To: Bill Moran <wmoran@collaborativefusion.com> Cc: freebsd-questions@freebsd.org, derek@computinginnovations.com Subject: Re: Purchasing the correct hardware: dual-core intel? Big cache? Message-ID: <444E364D.4000503@mac.com> In-Reply-To: <20060425095920.a8342390.wmoran@collaborativefusion.com> References: <20060424154617.9dc28c94.wmoran@potentialtech.com> <6.0.0.22.2.20060424175443.02927f48@mail.computinginnovations.com> <20060425084752.2453c0f1.wmoran@collaborativefusion.com> <6.0.0.22.2.20060425075227.028aea10@mail.computinginnovations.com> <20060425092526.6fe5efa6.wmoran@collaborativefusion.com> <444E28A5.3010902@mac.com> <20060425095920.a8342390.wmoran@collaborativefusion.com>
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Bill Moran wrote: > On Tue, 25 Apr 2006 09:48:21 -0400 > Chuck Swiger <cswiger@mac.com> wrote: [ ...long explanation snipped for brevity... :-) ] > Thanks, Chuck. Most welcome. > What I'm looking for is a way to measure this on the current machines > we're using so I can make a prediction as to whether larger cache > sizes will improve performance. What I'm looking for is some sort of > counter or the like that I can use to tell what my current L2 cache > hit ratio _is_, so I can intelligently speculate as to whether another > 6M of cache is worth the outrageous price. It's possible to write code which tests cache size and latency empirically, but I'm not sure how to obtain the ratio you're looking for directly for your particular workload. Previous experience suggests that large CPU cache helps heavily multithreaded or parallel multiprocess tasks by a lot, but does little to help something like a big database because the amount of data you have to traverse is much larger than will fit into any L2 cache, no matter how big. On the other hand, more L2 cache can provide more significant benefit to a well-tuned database if the indexes or particular frequently-used subqueries fit better into the larger cache... -- -Chuck
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