Matt Dillon <[EMAIL PROTECTED]> 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 ---- [EMAIL PROTECTED]
A master's secrets are only as good as
the master's ability to explain them to others.
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