[RFC] [0/5] tuning options for PPC64

[RFC] [0/5] tuning options for PPC64

[Marvin]

Hi,

the following five patches should lay a foundation to more fine-grained tuning 
on PPC64 cpus. They must be applied in order. The motivation are the 
discussions of serveral cpu specific optimizations in the past on this list, 
cleanup of the wired Makefile/CONFIG_POWERx constructs and at least the 
ownership of a PS3.

The patches intoduce CONFIG_TUNE_some_cpu and CONFIG_OPT_EXCLUSIVE, with the 
aim to cover two common cases:

	- distributions want a common kernel, bootable on all ppc64 machines and tune 
for a certain cpu

	- high end users don't care about older cpus and want to compile a kernel 
with their favorite mcpu option

I know there is also the possibility of mcpu=x and mtune=y, y>x but this can 
be tackled in the next step (hopefully).

I know this will bring up some conserns, but my initial findings grepping the 
defconfigs show:

	- CONFIG_POWER3 enables BATS only
		it is also used the enable some configs
		it is used always in combination with CONFIG_POWER4

	- CONFIG_POWER4 is always combined with CONFIG_PPC64 and vice versa
		all POWER3 || POWER4 || PPC64 can be replaced by PPC64

	- There seems to be no support for 32-bit kernels on ppc64 machines

I hope for some feedback, so this new scheme (or some other) can be included 
to mainstream kernel. 

Greetings

Marvin

Re: [RFC] [0/5] tuning options for PPC64

[Marvin]

Hi,

and thanks for the feedback. To make it short, the conclusions I draw from 
that are:

	- let the cpu type be choosen optionaly
	- both target cpu and tuning cpu should be selectable
	- if one cpu gets choosen, it should select some feature flag, mcpu and mtune 
option automatically in Kconfig.cputypes
	- if none gets choosen, all features will be selected (is this save?)

I found these ppc64 cpu specific candidates for CONFIG_FEATURE-X:

Altivec (G4, G5, POWER6+7, PA6T)
BAT64 aka POWER3 (Power3)
FPU (all)
Std_MMU (all)
Virt_CPU_Accounting (all, except PA6T?)
VSX (power7)

There are probably some more features present, which are currently enabled by 
some ifdefs for PPC64 and POWER4 (e.g. powermac/feature.c). I will not touch 
them due to my little knowledge and just keep these symbols.

I guess this will become another long weekend ;-)

Marvin


On Monday 21 July 2008 09:02:47 Marvin wrote:
> Hi,
>
> the following five patches should lay a foundation to more fine-grained
> tuning on PPC64 cpus. They must be applied in order. The motivation are the
> discussions of serveral cpu specific optimizations in the past on this
> list, cleanup of the wired Makefile/CONFIG_POWERx constructs and at least
> the ownership of a PS3.
>
> The patches intoduce CONFIG_TUNE_some_cpu and CONFIG_OPT_EXCLUSIVE, with
> the aim to cover two common cases:
>
> 	- distributions want a common kernel, bootable on all ppc64 machines and
> tune for a certain cpu
>
> 	- high end users don't care about older cpus and want to compile a kernel
> with their favorite mcpu option
>
> I know there is also the possibility of mcpu=x and mtune=y, y>x but this
> can be tackled in the next step (hopefully).
>
> I know this will bring up some conserns, but my initial findings grepping
> the defconfigs show:
>
> 	- CONFIG_POWER3 enables BATS only
> 		it is also used the enable some configs
> 		it is used always in combination with CONFIG_POWER4
>
> 	- CONFIG_POWER4 is always combined with CONFIG_PPC64 and vice versa
> 		all POWER3 || POWER4 || PPC64 can be replaced by PPC64
>
> 	- There seems to be no support for 32-bit kernels on ppc64 machines
>
> I hope for some feedback, so this new scheme (or some other) can be
> included to mainstream kernel.
>
> Greetings
>
> Marvin
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