[Info-vax] Unix on A DEC Vax?

[Simon Clubley]

On 2013-01-17, John Wallace <johnwallace4 at yahoo.co.uk> wrote:
>
> What kind of performance is reasonable to expect from emulated
> systems? I know that's a "how long is your piece of string" question,
> but is it answered anywhere,objectively or anecdotally?
>
> Someone I know earlier this week did a quick (and therefore not
> necessarily entirely valid) test of an existing mostly-computebound
> single-threaded workload on a well known commercial Alpha (not VAX)
> emulator. The workload was the only load on the emulator allegedly on
> a dedicated modern x86 server.
>
> The same workload was measured in its current natural environment, an
> AlphaServer 2100 5/250 (mid 1990s?) which was also supporting its
> usual interactive and batch workload (at the time of the tests a
> relatively light workload).
>
> The test workload on the emulator was three times slower (ie runtime
> three times longer), which was a bit of a surprise.
>

Was there any dynamic binary translation of the Alpha images going on ?

If this is a traditional repeated translation of the Alpha instructions
type emulator, I am actually a bit impressed it's only about three times
slower.

If the emulator is performing dynamic binary translation of the original
image, then, personally, I would have expected better performance, but I
don't have good enough knowledge of current translation technology to give
you any specific figures.

> Is that kind of performance degradation (vs the same workload on
> antique native hardware) to be expected? Does performance vary widely
> with different emulators? Does the host environment (e.g. VMware vs
> native) matter much?

Yes, performance does vary widely based on the type of emulator. Dynamic
translation should give you better overall performance for a number of
normal workloads, but at the expense of additional non-deterministic
performance behaviour.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
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