[PATCH] powerpc: Per process DSCR

[Kumar Gala]

On Nov 16, 2010, at 6:31 PM, Anton Blanchard wrote:

> In order to add per process control of the DSCR, the following patch emulates
> read/write of the DSCR from userspace and saves and restores it on context
> switch. We add emulated stats to track how many times we do this.
> 
> While writing this patch a few things were apparent:
> 
> - How will this work with the global DSCR setting in
>  /sys/devices/system/cpu/cpu*/dscr? Do we deprecate it? One thought is
>  to add a new sysfs entry (eg dscr_enabled), which tells us to
>  override any per process settings. Another way would be to overload
>  the dscr sysfs entry and make -1 mean the system wide dscr setting is
>  disabled.
> 
> - Do we need an out of band method of changing the DSCR so another
>  process or could modify it? We may want to modify the DSCR of a long
>  running process, eg a HPC job.
> 
> - To improve context switch speed we should probably check the old and
>  new DSCR values are identical and avoid the SPR write.
> 
> Signed-off-by: Anton Blanchard <anton at samba.org>

We don't have no stinking DSCR ;).  Would like this to be #ifdef CONFIG_PPC_BOOK3S_64.

- k