On Thu, 3 Nov 2016 02:32:39 -0400 "Shreyas B. Prabhu" <shreya...@gmail.com> wrote:
> 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. I see, that makes sense. Would it be possible to keep count of the number of threads going into winkle in core_idle_state? Even if that is not a guarantee if them requiring a PORE wakeup, would the restore case be harmful? Thanks, Nick
