Re: [REVIEW] Re: Compression of full-page-writes

On Tue, Sep 23, 2014 at 8:15 PM, Florian Weimer <fw@deneb.enyo.de> wrote:
> * Ants Aasma:
>
>> CRC has exactly one hardware implementation in general purpose CPU's
>
> I'm pretty sure that's not true.  Many general purpose CPUs have CRC
> circuity, and there must be some which also expose them as
> instructions.

I must eat my words here, indeed AMD processors starting from
Bulldozer do implement the CRC32 instruction. However, according to
Agner Fog, AMD's implementation has a 6 cycle latency and more
importantly a throughput of 1/6 per cycle. While Intel's
implementation on all CPUs except the new Atom has 3 cycle latency and
1 instruction/cycle throughput. This means that there still is a
significant handicap for AMD platforms, not to mention Power or Sparc
with no hardware support. Some ARM's implement CRC32, but I haven't
researched what their performance is.

Regards,
Ants Aasma
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