On Thu, Nov 3, 2016 at 2:17 AM, Nicholas Piggin <npig...@gmail.com> wrote: > 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. >
PACA_THREAD_IDLE_STATE will have what was 'requested'. It may not be the state we are waking up from. For example, if 7 threads of the core execute winkle instruction while 1 thread of the same core executes sleep. Here the core only enters sleep whereas PACA_THREAD_IDLE_STATE for the 7 threads will have PNV_THREAD_WINKLE. Thanks, Shreyas
