On Thu, 3 Nov 2016 01:56:46 -0400 "Shreyas B. Prabhu" <shreya...@gmail.com> wrote:
> On Thu, Nov 3, 2016 at 1:21 AM, Nicholas Piggin <npig...@gmail.com> wrote: > > On Wed, 2 Nov 2016 14:15:48 +0530 > > Gautham R Shenoy <e...@linux.vnet.ibm.com> wrote: > > > >> Hi Nick, > >> > >> On Wed, Nov 02, 2016 at 07:36:24PM +1100, Nicholas Piggin wrote: > >> > > >> > Okay, I'll work with that. What's the best way to make a P8 do > >> > winkle sleeps? > >> > >> From the userspace, offlining the CPUs of the core will put them to > >> winkle. > > > > Thanks for this. Hum, that r13 manipulation throughout the idle > > and exception code is a bit interesting. I'll do the minimal patch > > for 4.9, but what's the reason not to just use the winkle state > > in the PACA rather than storing it into HSPRG0 bit, can you (or > > Shreyas) explain? > > > Hi Nick, > > Before deep winkle, checking SRR1's wakeup bits (Bits 46:47) was enough to > figure out which idle state we are waking up from. But in P8, SRR1's wakeup > bits aren't enough since bits 46:47 are 0b11 for both fast sleep and > deep winkle. > So to distinguish bw fastsleep and deep winkle, we use the current HSPRG0/PORE > trick. We program the PORE engine (which is used for state restore when waking > up from deep winkle) to restore HSPRG0 with the last bit set (we do this in > pnv_save_sprs_for_winkle()). R13 bit manipulation in pnv_restore_hyp_resource > is related to this. Right, I didn't realize how that exactly worked until I had to go read the code just now. It's a neat little trick. I'm wondering can we use PACA_THREAD_IDLE_STATE==PNV_THREAD_WINKLE for this instead? It would just make the early PACA usage in the exception handlers able to use more common code. Thanks, Nick
