Date: Tue, 06 Mar 2001 07:46:37 -0500 From: Michael Sinz <msinz@wgate.com> To: hackers@FreeBSD.ORG Subject: Re: Machines are getting too damn fast Message-ID: <3AA4DC2D.F72208C7@wgate.com> References: <bulk.40201.20010305175418@hub.freebsd.org>
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Matt Dillon <dillon@earth.backplane.com> wrote: > Subject: Re: Machines are getting too damn fast > > :throughput. For example, on the PIII-850 (116MHz FSB and SDRAM, its > :overclocked) here on my desk with 256KB L2 cache: > : > :dd if=/dev/zero of=/dev/null bs=512k count=4000 > :4000+0 records in > :4000+0 records out > :2097152000 bytes transferred in 8.229456 secs (254834825 bytes/sec) > : > :dd if=/dev/zero of=/dev/null bs=128k count=16000 > :16000+0 records in > :16000+0 records out > :2097152000 bytes transferred in 1.204001 secs (1741819224 bytes/sec) > : > :Now THAT is a significant difference. :-) > > Interesting. I get very different results with the 1.3 GHz P4. The > best I seem to get is 1.4 GBytes/sec. I'm not sure what the L2 cache > is on the box, but it's definitely a consumer model. > > dd if=/dev/zero of=/dev/null bs=512k count=4000 > 2097152000 bytes transferred in 2.363903 secs (887156520 bytes/sec) > > dd if=/dev/zero of=/dev/null bs=128k count=16000 > 2097152000 bytes transferred in 1.471046 secs (1425619621 bytes/sec) > > If I use lower block sizes the syscall overhead blows up the > performance (it gets lower rather then higher). So I figure I don't > have as much L2 as on your system. The P4 has other issues when you don't do straight line code. Any branch mis-predictions cost a minimum of 20 cycles due to the pipeline plus whatever cache/fetch/decode hits you may get on the actual target. This may be why you get lower values than a PIII or Athelon. (Both have significantly lower penalty for branch mis-prediction) -- Michael Sinz ---- Worldgate Communications ---- msinz@wgate.com A master's secrets are only as good as the master's ability to explain them to others. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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