Re: [Linux-ia64] page size > 16KB

From: Mario Smarduch <cms063_at_email.mot.com>
Date: 2003-03-14 07:44:27
David Mosberger wrote:

> >>>>> On Wed, 12 Mar 2003 13:51:16 -0600, Mario Smarduch <cms063@email.mot.com> said:
>
>   Mario> Hi David, I'm very curious about your statement regarding
>   Mario> reproducible results - a desirable attribute for many
>   Mario> applications in our case soft real-time predictability. With
>   Mario> the caches on Itanium2 being highly associative, did you
>   Mario> notice a dramatic change in reproducibility as you did in TLB
>   Mario> efficiency? This is assuming a locked memory intensive
>   Mario> application or this was too long ago for you to remember :)
>
> Heh, I barely remember what I ate for dinner last night, so I
> certainly don't remember what that application was about... ;-)
>
> Apps with large arrays certainly can see significant variation due to
> lack of page coloring in the kernel, even with high associativity.  I
> ran a Monte Carlo simulation on this a while ago and attached the
> results below.
>
> As you can see, high associativity keeps page-coloring effects away up
> until you occupy about 1.5-2MB (out of a 3MB cache).  So if you have,
> say, a 3MB array, you'd clearly expect to see page-coloring effects.

David,
    thanks for pulling this up -  its very interesting. For 12-way associtivity
64KB pg size does stand out quite a bit from 4,8,16KB, although the effect
appears to be more visual because 32KB is not supported.

>
>
> The graph also shows that larger page sizes somewhat reduce the
> negative effets of lack of page-coloring (not entirely intuitive, but
> it's pretty complex as to what's going on, so it's not surprising that
> intuition doesn't get us very far).

yes its a very painful graph to look at :)

- Mario.

>
>
> I should update the graph for Madison some day.
>
>         --david
>
>   ------------------------------------------------------------------------
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>            Description: coll.pdf
Received on Thu Mar 13 12:48:08 2003

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