Re: Where to call L2 cache enabling code from?

[Dave Jones]

On Fri, Apr 14, 2006 at 12:49:49PM -0400, Steve Snyder wrote:
 > On Friday 14 April 2006 11:46 am, Alan Cox wrote:
 > > On Gwe, 2006-04-14 at 11:05 -0400, Steve Snyder wrote:
 > > > I have a machine in which the BIOS does not enable the Pentium3's L2
 > > > cache at boot time.  At what point in the kernel init process
 > > > can/should I call the code to enable the cache?
 > >
 > > What part of the cache setup is not done correctly ? The mtrr registers
 > > or other things ?
 > 
 > It's not that the kernel is failing in any respect.  The BIOS simply does 
 > not enable the on-CPU L2 cache at power-on.  (The machine originally 
 > shipped with a Pentium2, and doesn't know how to enable the L2 cache on 
 > the Pentium3 that is now running in it.)
 > 
 > I've got a small device driver that enables the L2 cache.  It works fine 
 > when build as a module and loaded after booting has completed.  My goal 
 > is to move the code into the kernel so that it is run early in the kernel 
 > init process.  I expect that having the L2 cache go from "0KB" to 256KB 
 > will improve boot time greatly, as well as informing the kernel from the 
 > get-go of the true capabilities of this processor.
 > 
 > Getting the code into the kernel image is a no-brainer.  But once it is 
 > built into the kernel, at what point should I call it?

arch/i386/kernel/cpu/intel.c has a bunch of workarounds for various
issues.  Is there a valid use-case for ever booting with cache disabled
though? If so, this should probably be a boot-time option to enable it.

		Dave

-- 
http://www.codemonkey.org.uk
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