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Date:      Tue, 24 Apr 2007 23:13:59 +0200
From:      Ivan Voras <ivoras@fer.hr>
To:        freebsd-questions@freebsd.org
Subject:   Re: Memory >3.5GB not used?
Message-ID:  <f0lrup$18a$1@sea.gmane.org>
In-Reply-To: <20070424145433.734761db.wmoran@potentialtech.com>
References:  <01d301c78699$d6a36820$0300020a@mickey>	<20070424140528.95287ff4.wmoran@potentialtech.com>	<021201c7869f$ee90fd70$0300020a@mickey>	<3ee9ca710704241144n4ab349c6m901586e427b1ae0d@mail.gmail.com>	<021c01c786a0$fe7e5510$0300020a@mickey> <20070424145433.734761db.wmoran@potentialtech.com>

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Bill Moran wrote:
> In response to "Don O'Neil" <lists@lizardhill.com>:
>=20
>> I never had this problem before when I built the kernel the first time=
=2E
>> Could my module source be corrupt? If so, how do I re-install just the=

>> kernel sources for 6.1?
>=20
> Not all modules work with PAE.  Read the example PAE kernel file for
> information.
>=20
> 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      INDE=
X

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
                                                                 =3D=3D=3D=
=3D=3D=3D=3D=3D=3D
     FINAL SCORE                                                     317.=
2



NO PAE:
                     INDEX VALUES
TEST                                        BASELINE     RESULT      INDE=
X

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
                                                                 =3D=3D=3D=
=3D=3D=3D=3D=3D=3D
     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.


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