[Skiboot] [PATCH v2] SLW: Remove stop1_lite and stop2_lite

[Nicholas Piggin]

On Wed, 23 May 2018 14:49:29 +0530
Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com> wrote:

> * Akshay Adiga <akshay.adiga at linux.vnet.ibm.com> [2018-05-23 13:47:38]:
> 
> Lite stop states are designed to stop dispatch of instructions but not
> relinquish thread resources.  They primarily reduce switching power
> with a benefit of resuming operation without any state loss.  This
> could save upto a micro-second in wakeup latency. However there is
> a down side to this. Since thread resources are not relinquished,
> other running threads in the core cannot benefit from automatically
> folding down to lower SMT mode.
> 
> We have stop0_lite and stop1_lite that are pretty close in operational
> characteristics, hence we can choose to keep only stop0_lite and
> remove stop1_lite.
> 
> However, stop2_lite provides some minimal benefits over stop2. But
> since the wakeup latency of stop2 to re-clock the core is 10-20us, the
> context preservation benefit is reduced.
> 
> This patch removes all stop_lite states except stop0_lite.  We should
> re-introduce stop2_lite once kernel cpuidle governor can understand
> SMT folding thresholds and auto promote to a non-lite state.
> 
> > Signed-off-by: Akshay Adiga <akshay.adiga at linux.vnet.ibm.com>  
> 
> Reviewed-by: Vaidyanathan Srinivasan <svaidy at linux.vnet.ibm.com>

Reviewed-by: Nicholas Piggin <npiggin at gmail.com>