[Beowulf] Moores Law is dying

Bruno Coutinho coutinho at dcc.ufmg.br
Wed Apr 15 14:04:13 PDT 2009


2009/4/14 Joe Landman <landman at scalableinformatics.com>

> Jon Forrest wrote:
>
>  But this wouldn't happen in the scenarios you describe
>> because text is read-only. There would be no updaters or writers
>> or any kind of contention. The text pages would have to get filled
>>
>
> Ok, lets assume you have a table in the text, that every thread is using to
> dereference.  Sure it can go in the data section, but some compilers (old
> SGI) could leave it in the text area for faster access.


I believe that today it can't be done. In most architectures (except for our
lovely x86 :) ) text pages are read only so data placed here must be read
only.


>
>
> Same thing with contention.  Read contention is harder to diagnose than
> write contention, as you don't get the cache line update from the writes
> triggering the associated counters, so this is a bit more subtle.  But the
> effect is there.


This can be relived with broadcast hardware, but this can make hardware
complexity grow too fast.


>
>
> [...]
>
>  I know you might postulate that 32 bit text is effectively the CS
>>> equivalent of "C" in physics ... you may approach it asymptotically, but
>>> never actually get there ... but unlike in physics, there isn't really an
>>> underlying reason why you might not get there.
>>>
>>
>> The underlying reason in this case is complexity.
>>
>
> So you are posulating that complexity scales as Nbytes of text?
>
>
>> Jon
>>
>>
>
> --
> Joseph Landman, Ph.D
> Founder and CEO
> Scalable Informatics LLC,
> email: landman at scalableinformatics.com
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