amd k6-3 L3 cache

amd k6-3 L3 cache

[Peter Rabbitson]

Hi everyone. I have a question regarding hardware caches. When I compile the
kernel on k6/2 cpu I get messages identifying L1 cache of 64k and L2 cache of
1024k which are the actual hardware amounts. But kernel on a k6/3+ cpu gives
out this:
-------
CPU: L1 I Cache: 32K (32 bytes/line), D cache 32K (32 bytes/line)
CPU: L2 Cache: 256K (32 bytes/line)
CPU: After vendor init, caps: 008021bf c08029bf 00000000 00000002
CPU:     After generic, caps: 008021bf c08029bf 00000000 00000002
CPU:             Common caps: 008021bf c08029bf 00000000 00000002
------
Does this mean that I am actually loosing the benefit of having 1m of cache 
on the motherboard (in this case L3)? Or the kernel still uses transparrent
bios routines and stores data in L3? Or maybe such cpus shopuld run kernel
compiled for k7/athlon cpus? I would appreciate any comments or suggestions,
nevertheless I am more than non-proficient in programming. Just a curious
cat in the linux community :)

Peter

Re: amd k6-3 L3 cache

[Dave Jones]

On Tue, Jun 04, 2002 at 11:46:16PM -0500, Peter Rabbitson wrote:
 > Hi everyone. I have a question regarding hardware caches. When I compile the
 > kernel on k6/2 cpu I get messages identifying L1 cache of 64k and L2 cache of
 > 1024k which are the actual hardware amounts. But kernel on a k6/3+ cpu gives

L1/L2 cache is on CPU. L3 is on motherboard. The kernel only reports
(and cares about) L1/L2 (And then asides from informational purposes,
i.e. /proc/cpuinfo, it's only used for anything useful under SMP which isn't
an issue for K6-3)

The L3 is being used transparently, with no need for any support by
the kernel. (As long as it's been enabled by the BIOS)

        Dave

-- 
| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

Re: amd k6-3 L3 cache

[Rene Rebe]

Hi.

On: Tue, 4 Jun 2002 23:46:16 -0500,
    Peter Rabbitson <rabbit@rabbit.online.bg> wrote:
> Hi everyone. I have a question regarding hardware caches. When I compile the
> kernel on k6/2 cpu I get messages identifying L1 cache of 64k and L2 cache of
> 1024k which are the actual hardware amounts. But kernel on a k6/3+ cpu gives
> out this:
> -------
> CPU: L1 I Cache: 32K (32 bytes/line), D cache 32K (32 bytes/line)
> CPU: L2 Cache: 256K (32 bytes/line)
> CPU: After vendor init, caps: 008021bf c08029bf 00000000 00000002
> CPU:     After generic, caps: 008021bf c08029bf 00000000 00000002
> CPU:             Common caps: 008021bf c08029bf 00000000 00000002
> ------

This are the correct values - I do not know why a K6/2 kernel reports
bogus ones.

The caches (incl. the L3 cache on the mainboard) are used by the
silicon logic in you CPU and chipset automatically - no OS or BIOS
support is needed for this.

> Does this mean that I am actually loosing the benefit of having 1m of cache 
> on the motherboard (in this case L3)? Or the kernel still uses transparrent
> bios routines and stores data in L3? Or maybe such cpus shopuld run kernel
> compiled for k7/athlon cpus? I would appreciate any comments or suggestions,
> nevertheless I am more than non-proficient in programming. Just a curious
> cat in the linux community :)
> 
> Peter

k33p h4ck1n6
  René

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