Re: AMD64 VS EM64T
On Thu, 02 Dec 2004 15:41:10 -0600, Jin Zhao <jzhao@qcorps.com> wrote:
> I am currently faced with choosing one of them as our forthcoming 64 bit
> platform. So far I read a couple of reviews, most of which seems favor
> AMD64 a little bit. I also did some initial testings on an opteron box
> with Debian pure64 unstale. So far it looks good.
>
> The price differrence is not a big issue. The most important are
> performance, reliability and compatibility, esp on Linux, most likely
> Debian. We will use them to run server side java applicaitons.
>
> Redhat mentioned this in their realease statement:
> "Software IOTLB — Intel EM64T does not support an IOMMU in hardware
> while AMD64 processors do. This means that physical addresses above 4GB
> (32 bits) cannot reliably be the source or destination of DMA
> operations. Therefore, the Red Hat Enterprise Linux 3 Update 2 kernel
> "bounces" all DMA operations to or from physical addresses above 4GB to
> buffers that the kernel pre-allocated below 4GB at boot time. This is
> likely to result in lower performance for IO-intensive workloads for
> Intel EM64T as compared to AMD64 processors."
>
> This issue may affect database usage, but probably not a java
> applicaiton server. There might be other unkown issues as well. I am
> eager to know what are the Debian team and users' point on these two
> platforms, esp those who already used them.
AMD's original implementation of their AMD64 architecture is gauged as
superior engineering-wise by many hardware reviewers.
The Intel implementation still suffers from bandwidth starvation as
the same bus architecture as of old is still being used. This causes
problems when you get more processors and memory, which the AMD
implementation solves by making each processor have its own set of
memory and resources.
--
Paolo Alexis Falcone
pfalcone@gmail.com
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