Memory >3.5GB not used?
Bill Moran
wmoran at potentialtech.com
Tue Apr 24 22:20:35 UTC 2007
In response to Ivan Voras <ivoras at fer.hr>:
> Bill Moran wrote:
> > In response to "Don O'Neil" <lists at lizardhill.com>:
> >
> >> I never had this problem before when I built the kernel the first time.
> >> Could my module source be corrupt? If so, how do I re-install just the
> >> kernel sources for 6.1?
> >
> > Not all modules work with PAE. Read the example PAE kernel file for
> > information.
> >
> > PAE is an awful hack, BTW. I've heard a number of people complain that
> > performance sucks under PAE.
>
> It greatly depends on the workload. For example, these are my results
> with unixbench:
>
>
> PAE:
> INDEX VALUES
> TEST BASELINE RESULT INDEX
>
> Dhrystone 2 using register variables 116700.0 6404191.9 548.8
> Double-Precision Whetstone 55.0 1444.6 262.7
> Execl Throughput 43.0 2374.5 552.2
> File Copy 1024 bufsize 2000 maxblocks 3960.0 47618.0 120.2
> File Copy 256 bufsize 500 maxblocks 1655.0 41809.0 252.6
> File Copy 4096 bufsize 8000 maxblocks 5800.0 58002.0 100.0
> Pipe Throughput 12440.0 1018477.4 818.7
> Pipe-based Context Switching 4000.0 32811.6 82.0
> Process Creation 126.0 4491.9 356.5
> Shell Scripts (8 concurrent) 6.0 638.0 1063.3
> System Call Overhead 15000.0 798137.5 532.1
> =========
> FINAL SCORE 317.2
>
>
>
> NO PAE:
> INDEX VALUES
> TEST BASELINE RESULT INDEX
>
> Dhrystone 2 using register variables 116700.0 6673515.4 571.9
> Double-Precision Whetstone 55.0 1475.1 268.2
> Execl Throughput 43.0 2335.9 543.2
> File Copy 1024 bufsize 2000 maxblocks 3960.0 43796.0 110.6
> File Copy 256 bufsize 500 maxblocks 1655.0 39474.0 238.5
> File Copy 4096 bufsize 8000 maxblocks 5800.0 57819.0 99.7
> Pipe Throughput 12440.0 998089.5 802.3
> Pipe-based Context Switching 4000.0 25928.4 64.8
> Process Creation 126.0 5043.9 400.3
> Shell Scripts (8 concurrent) 6.0 697.0 1161.7
> System Call Overhead 15000.0 792628.3 528.4
> =========
> FINAL SCORE 312.7
>
> The final score is better in PAE case because IO performance measured
> better, but in this case I know this particular benchmark can be
> ignored, but the rest of the numbers should be fine.
>
> In short, PAE is worse, but not horribly so.
Does this test demonstrate usage of memory over 4G? It's my understanding
that PAE starts to suffer when it has to look at the memory over 4G (which
is the problem it's intended to solve)
If your entire test fits in under 4G, you're not seeing the worst of it.
At least, that's my understanding of the issue.
--
Bill Moran
http://www.potentialtech.com
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