pae kernel

[FritoBandito]

I understand that the pae kernel allows for the use of >4gb of ram. I have 4 gigs of ram + 512 mb video memory which i believe is limited by the kernel.

So I would have access to a little more ram if i used the pae kernel.
My question is are there any downsides to using it?
If there are no downsides why is there a non pae kernel?

[menotu]

I haven't seen/heard of any downsides to using it - I use it as my kernel of choice.

[Old-Polack]

Same here.

[root@fatman ~]# uname -r
2.6.38.1-pclos2.pae

[AS]

Hi,

pae kernel is so called because it use a particular feature of the CPU (Physical Address Extension), which allow for addressing up to 64Gb RAM,
although pae is present on all recent CPUs, is not available on all CPUs.

Other than the above, actually the differences are related to Kernel Interrupt time actually set to 100 Hz in pae version, and set to 1000 Hz in all other PCLinuxOS versions,
(an higher interrupt frequency allow for faster kernel reaction upon interrupts, may be useful for some applications that require realtime response),
other difference are related to the default scheduler (bfs vs. cfq), one version, a64, is optimized for AMD 64 bit CPUs.

The 512 Mb video-card memory, are unaffected by the kernel choice.

Unless you have specific reason to require bfs scheduler and 1000 Hz frequency, there are no drawbacks using pae kernels.

AS

[Neal ManBear]

If there are no downsides why is there a non pae kernel?

Why? Because not every user has 4 GB or more RAM. It is not really common to have that much RAM at this time.

[muungwana]

If you look at linux's kernel configuration options, you will see that the kernel can be configured to use up to 896MB of memory, upto 4GB of memory and upto 64GB of memory(pae kernel).

With a 32 bit operating system, the system can see a maximum of 4GB and that means the remaining 60GB will somehow first be remapped into the 4GB before it can be accessed and this costs CPU cycles and slows things down.

[jaydot]

i'm using a bfs kernel, which claims (and does) to support 4gb.  which of pae/bfs is the better option, or does it make a difference?

[Texstar]

i'm using a bfs kernel, which claims (and does) to support 4gb.  which of pae/bfs is the better option, or does it make a difference?

What about a pae.bfs kernel! Yeh, you get all the performance of bfs plus the extra memory available without a performance hit. Seriously there is not much difference between the kernels anymore. I am using the pae.bfs kernel from the PASS server. The reason is I get 400mb more of free memory with pae.bfs than with just bfs on my 4 gig box.

[Was_Just19]

I have a P4 machine here which appears to be limited by Dell ......  it sees about 3.6GB of the 4 installed using the bfs kernel, but sees less when using the pae kernel .......  I guess due to the extra overhead of the pae kernel.

[menotu]

Having that bit more memory available on the pae kernel can also be useful when running Virtualbox.

[Texstar]

I have a P4 machine here which appears to be limited by Dell ......  it sees about 3.6GB of the 4 installed using the bfs kernel, but sees less when using the pae kernel .......  I guess due to the extra overhead of the pae kernel.

I get 3.4 with bfs and 3.8 with pae.

[ayearhasgone]

Quite honestly if you need to use more than 4 GBs of RAM, you should stop and think about your life for a minute.  Maybe I just remember the good ol' days when 512 MBs of RAM was top of the line, but 4 gigs is a LOT of RAM for a home desktop.

My old lappy shipped with 4 gigs and everyone was telling me to install 64-bit distro's.  I always found myself having hardware problems (CD drive not ejecting, shaky wifi) that I never had with 32-bit distro's.  One day I realized that I was only using maybe 1 gig at a time, so I installed 32-bit and never looked back.

Point is, pick which kernel is best for you.  You probably don't need to utilize a full 4 gigs of RAM.

[FritoBandito]

Are you sure that the 4GB ram limit doesn't include video ram? It does on windows computers and I assume they would both have the same 32-bit cap. Addressing limits *waves hands*

so the downside is that:
there is more overhead

I have a P4 machine here which appears to be limited by Dell ......  it sees about 3.6GB of the 4 installed using the bfs kernel, but sees less when using the pae kernel .......  I guess due to the extra overhead of the pae kernel.

and it reacts slightly slower which humans would never notice

Other than the above, actually the differences are related to Kernel Interrupt time actually set to 100 Hz in pae version, and set to 1000 Hz in all other PCLinuxOS versions,
(an higher interrupt frequency allow for faster kernel reaction upon interrupts, may be useful for some applications that require realtime response),
other difference are related to the default scheduler (bfs vs. cfq), one version, a64, is optimized for AMD 64 bit CPUs.

[AS]

and what report the command free, using pae.bfs kernel ?

AS

[Was_Just19]

I made a mistake and deleted my previous post.
The kernels did not correctly install and I forgot to check which one I was using 

While preparing for installation:

kernel-2.6.38.2-pclos1.pae.bfs-1-1pclos2011
INTERNAL ERROR: hd0 has no mapping in device.map (when translating (hd0,5))
MDK::Common::Various::internal_error() called from /usr/lib/libDrakX/bootloader.pm:1610
bootloader::grub2dev_and_file() called from /usr/lib/libDrakX/bootloader.pm:1619
bootloader::grub2dev() called from /usr/lib/libDrakX/bootloader.pm:245
bootloader::_may_fix_grub2dev() called from /usr/lib/libDrakX/bootloader.pm:220
bootloader::read_grub() called from /usr/lib/libDrakX/bootloader.pm:174
bootloader::read() called from /usr/sbin/bootloader-config:64
kernel-devel-2.6.38.2-pclos1.pae.bfs-1-1pclos2011