Pentium IV Xeon memory bandwidth. Any experience?

Richard Walsh rbw at networkcs.com
Mon Jun 25 14:56:58 EDT 2001


On Mon, 25 Jun 2001, Greg Lindahl wrote:

> On Mon, Jun 25, 2001 at 02:19:15PM +0200, Thomas Guignon wrote:
>
> > We have tested and 1.2 Ghz with PC2100 DDR with Level 1 Blas and results are
> > quite nice:
> > -dnrm2: (one vector read)
> > 1450 10^6 B/s
> > -ddot: (two vector read)
> > 1040 10^6 B/s
> > -daxpy (one vector read and one vector read/write)
> > 1150 10^6 B/s
> > - copy  (one vector read and one vector write)
> > 990 10^6 B/s
>
> These numbers look like they are for vectors that fit into cache.
>
> What does the STREAM benchmark report for this board? I bet it's
> substantially slower, and the person asking the question wanted main
> memory bandwidth, not cached bandwidth.


All, in testing done for the Anandtech reviews, bandwidth from L1, L2, and
memory is as follows:

L1

Read      Athlon 1.33   12467  MB/s
Read      P4     1.70   12555  MB/s

Write     Athlon 1.33   10140  MB/s
Write     P4     1.70    5663  MB/s

L2

Read      Athlon 1.33    4066  MB/s
Read      P4     1.70    6836  MB/s

Write     Athlon 1.33    4054  MB/s
Write     P4     1.33    5697  MB/s

Memory (stream-like test)

Single CPU P4    1.70    1318 MB/s
Dual   CPU P4    1.70    1361 MB/s

Single CPU Athln 1.20     694 MB/s (760 MP chipset)
Dual   CPU Athln 1.20     951 MB/s (760 MP chipset)

The BLAS numbers above suggest some cache effects
but they are not consistant with full cache speeds
if the Anandtech data is correct.

And on a related note ...

On a clock parity basis the Athlon has lower latencies
at most data sizes all the way out to memory; however,
the P4 compensates for this by having a larger maximum 
clock (1.7 vs 1.33).

Hope this is useful,

rbw

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