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

From: David Mosberger <davidm_at_napali.hpl.hp.com>
Date: 2003-03-14 05:05:22
>>>>> 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.

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).

I should update the graph for Madison some day.

	--david




Received on Thu Mar 13 10:06:59 2003

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