Alan L Tyree <[email protected]> writes:
> On Wed, 28 Oct 2009 10:39:48 +1100
> Robert Collins <[email protected]> wrote:
>
>> On Tue, 2009-10-27 at 13:15 +1100, Bill Donoghoe wrote:
>> >
>> > 1. What do I need to do to get Ubuntu to use 4Gb RAM? My current
>> > Jaunty installation only recognises around 3Gb. Is this just a kernel
>> > upgrade or ....
>>
>> If I remember correctly we don't support > 3GB on 32-bit installs
>> anymore - the performance overhead is terrible.
[...]
> al...@stormy:~/data$ uname -a
> Linux stormy 2.6.26-2-686-bigmem #1 SMP Sat Oct 17 18:25:48 UTC 2009
> i686 GNU/Linux
>
> I haven't noticed any performance hit. Box is Intel(R) Core(TM)2 Duo CPU
> E8400 @ 3.00GHz with 4GB of memory. My stuff is mostly NOT cpu intensive,
> but I do an occasional compile (LyX) and LaTeX large documents. No
> observable change.
It is there; the two common problems are that low memory fills, causing extra
competition, and that your memory bandwidth is terribly reduced through extra
TLB flushing to bounce data up above the easy line.
You probably don't notice any performance hit because, frankly, almost every
computer you can buy — including the one in your mobile phone — is
sufficiently overpowered for the work it is asked to do[1] that you can
sacrifice ten or twenty percent of performance[2] without noticing.
Daniel
Footnotes:
[1] ...most of the time; 3D games and some science work do push the limits.
Most regular desktop use doesn't.
[2] Typically, this is more than running the 32-bit bigmem kernel costs.
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