On Thu, 9 Aug 2018 20:15:04 +0530
Gautham R Shenoy <e...@linux.vnet.ibm.com> wrote:
> Hello Nicholas,
> On Fri, Aug 03, 2018 at 02:13:50PM +1000, Nicholas Piggin wrote:
> > Reimplement Book3S idle code in C, moving POWER7/8/9 implementation
> > speific HV idle code to the powernv platform code. Generic book3s
> > assembly stubs are kept in common code and used only to save and
> > restore the stack frame and non-volatile GPRs just before going to
> > idle and just after waking up, which can return into C code.
> >
> > Moving the HMI, SPR, OPAL, locking, etc. to C is the only real
> > way this stuff will cope with non-trivial new CPU implementation
> > details, firmware changes, etc., without becoming unmaintainable.
> >
> > This is not a strict translation to C code, there are some
> > differences.
> >
> > - Idle wakeup no longer uses the ->cpu_restore call to reinit SPRs,
> > but saves and restores them all explicitly.
> >
> > - The optimisation where EC=ESL=0 idle modes did not have to save
> > GPRs or change MSR is restored, because it's now simple to do.
> > State loss modes that did not actually lose GPRs can use this
> > optimization too.
> >
> > - KVM secondary entry code is now more of a call/return style
> > rather than spaghetti. nap_state_lost is not required beccause
> > KVM always returns via NVGPR restorig path.
> >
> > This seems pretty solid, so needs more review and testing now. The
> > KVM changes are pretty significant and complicated. POWER7 needs to
> > be tested too.
> >
> > Open question:
> > - Why does P9 restore some of the PMU SPRs (but not others), and
> > P8 only zeroes them?
>
> We are restoring MMCR0 (from the value saved in the stack) and MMCR1,
> MMCR2, and MMCRA in the stop_sprs in PACA. We saw that MMCRH and MMCRC
> are cleared on both POWER8 and POWER9. Hence we didn't restore
> them. MMCRS is being initialized by the KVM code.
>
> Is there anything apart from these that need to be restored ?
No I'm wondering why it is we restore those on POWER9? POWER8 does not
restore them, only zeroes. What is the difference with POWER9?
I will leave that in for now so we don't change too much with one patch,
but it would be nice to document a bit better the reasons for saving or
clearing SPRs.
>
> >
> > Since RFC v1:
> > - Now tested and working with POWER9 hash and radix.
> > - KVM support added. This took a bit of work to untangle and might
> > still have some issues, but POWER9 seems to work including hash on
> > radix with dependent threads mode.
> > - This snowballed a bit because of KVM and other details making it
> > not feasible to leave POWER7/8 code alone. That's only half done
> > at the moment.
> > - So far this trades about 800 lines of asm for 500 of C. With POWER7/8
> > support done it might be another hundred or so lines of C.
> >
> > Since RFC v2:
> > - Fixed deep state SLB reloading
> > - Now tested and working with POWER8.
> > - Accounted for most feedback.
> >
> > Since RFC v3:
> > - Rebased to powerpc merge + idle state bugfix
> > - Split SLB flush/restore code out and shared with MCE code (pseries
> > MCE patches can also use).
> > - More testing on POWER8 including KVM with secondaries.
> > - Performance testing looks good. EC=ESL=0 is about 5% faster, other
> > stop states look a little faster too.
> > - Adjusted SPR saving to handler POWER7, haven't tested it.
>
>
> This patch looks good to me.
>
> A couple of comments below.
>
> > ---
>
> [... snip ..]
>
> > @@ -178,23 +177,30 @@ struct paca_struct {
> > #endif
> >
> > #ifdef CONFIG_PPC_POWERNV
> > - /* Per-core mask tracking idle threads and a lock bit-[L][TTTTTTTT] */
> > - u32 *core_idle_state_ptr;
> > - u8 thread_idle_state; /* PNV_THREAD_RUNNING/NAP/SLEEP */
> > - /* Mask to indicate thread id in core */
> > - u8 thread_mask;
> > - /* Mask to denote subcore sibling threads */
> > - u8 subcore_sibling_mask;
> > - /* Flag to request this thread not to stop */
> > - atomic_t dont_stop;
> > - /* The PSSCR value that the kernel requested before going to stop */
> > - u64 requested_psscr;
> > + /* PowerNV idle fields */
> > + /* PNV_CORE_IDLE_* bits, all siblings work on thread 0 paca */
> > + unsigned long idle_state;
> > + union {
> > + /* P7/P8 specific fields */
> > + struct {
> > + /* PNV_THREAD_RUNNING/NAP/SLEEP */
> > + u8 thread_idle_state;
> > + /* Mask to indicate thread id in core */
> > + u8 thread_mask;
>
> This is no longer needed. We can get this from cpu_thread_in_core()
> from the C code.
>
> The only place where we are currently using this is to DUMP the value
> of the thread_mask from xmon but not anywhere else in the idle entry
> code.
Good catch, removed it.
> > + /* Mask to denote subcore sibling threads */
> > + u8 subcore_sibling_mask;
> > + };
> >
> > - /*
> > - * Save area for additional SPRs that need to be
> > - * saved/restored during cpuidle stop.
> > - */
> > - struct stop_sprs stop_sprs;
> > + /* P9 specific fields */
> > + struct {
> > +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> > + /* The PSSCR value that the kernel requested before
> > going to stop */
> > + u64 requested_psscr;
> > + /* Flag to request this thread not to stop */
> > + atomic_t dont_stop;
> > +#endif
> > + };
> > + };
> > #endif
> [..snip..]
>
> > --- a/arch/powerpc/kernel/exceptions-64s.S
> > +++ b/arch/powerpc/kernel/exceptions-64s.S
> > @@ -136,8 +136,9 @@ TRAMP_KVM(PACA_EXNMI, 0x100)
> >
> > #ifdef CONFIG_PPC_P7_NAP
> > EXC_COMMON_BEGIN(system_reset_idle_common)
> > - mfspr r12,SPRN_SRR1
> > - b pnv_powersave_wakeup
> > + mfspr r3,SPRN_SRR1
> > + bltlr cr3 /* no state loss, return to idle caller */
>
> So, if we are in an ESL=EC=0 stop, and we get an xscom SRESET,
> I guess the expected value in SPRN_SRR1[46:47] will be
> SRR1_WS_NOLOSS.
Yes it should, because ESL=0.
>
> In this case, though the LR would correspond to the caller of
> isa3_idle_stop_noloss(), r3 would have SPRN_SRR1 as opposed to 0 which
> is what we would have returned from isa3_idle_stop_noloss().
>
> Do we use the value to service the NMI ?
Yes. System reset exception is cleared when the interrupt is delivered
so we can't ignore it.
>
> > + b idle_return_gpr_loss
> > #endif
> >
> > /*
> > @@ -416,17 +417,17 @@ EXC_COMMON_BEGIN(machine_check_idle_common)
> > * Then decrement MCE nesting after finishing with the stack.
> > */
> > ld r3,_MSR(r1)
> > + ld r4,_LINK(r1)
> >
> > lhz r11,PACA_IN_MCE(r13)
> > subi r11,r11,1
> > sth r11,PACA_IN_MCE(r13)
> >
> > - /* Turn off the RI bit because SRR1 is used by idle wakeup code. */
> > - /* Recoverability could be improved by reducing the use of SRR1. */
> > - li r11,0
> > - mtmsrd r11,1
> > -
> > - b pnv_powersave_wakeup_mce
> > + mtlr r4
> > + rlwinm r10,r3,47-31,30,31
> > + cmpwi cr3,r10,2
>
> Can we use SRR1_WS_GPRLOSS here as well as in IDLETEST() ?
You mean
cmpwi cr3,r10,SRR1_WS_GPRLOSS >> (63-47)
>
> > + bltlr cr3 /* no state loss, return to idle caller */
> > + b idle_return_gpr_loss
>
> [..snip..]
>
> > +_GLOBAL(isa206_idle_insn_mayloss)
> > + std r1,PACAR1(r13)
> > + mflr r4
> > + mfcr r5
> > + /* use stack red zone rather than a new frame */
> > + addi r6,r1,-INT_FRAME_SIZE
> > + SAVE_GPR(2, r6)
> > + SAVE_NVGPRS(r6)
> > + std r4,_LINK(r6)
> > + std r5,_CCR(r6)
> > + cmpwi r3,PNV_THREAD_NAP
> > + bne 1f
> > + IDLE_STATE_ENTER_SEQ_NORET(PPC_NAP)
>
> We can have the following here, since we don't expect to return from
> nap.
>
> b . /* catch bugs */"
>
> > +1: cmpwi r3,PNV_THREAD_SLEEP
Sure, added.
> [..snip..]
>
> > +static unsigned long power7_idle_insn(unsigned long type)
> > +{
> > + int cpu = raw_smp_processor_id();
> > + int first = cpu_first_thread_sibling(cpu);
> > + unsigned long thread = 1UL << cpu_thread_in_core(cpu);
> > + unsigned long *state = &paca_ptrs[first]->idle_state;
> > + unsigned long srr1;
> > + bool full_winkle;
> > + struct p7_sprs sprs;
> > + bool sprs_saved = false;
> > + int rc;
> > +
> > + memset(&sprs, 0, sizeof(sprs));
> > +
> > + if (unlikely(type != PNV_THREAD_NAP)) {
> > + atomic_lock_thread_idle();
> > +
> > + BUG_ON(!(*state & thread));
> > + *state &= ~thread;
> > +
> > + if (power7_fastsleep_workaround_entry) {
> > + if ((*state & ((1 << threads_per_core) - 1)) == 0) {
> > + rc = opal_config_cpu_idle_state(
> > + OPAL_CONFIG_IDLE_FASTSLEEP,
> > + OPAL_CONFIG_IDLE_APPLY);
> > + BUG_ON(rc);
> > + }
> > + }
> > +
> > + if (type == PNV_THREAD_WINKLE) {
> > + sprs.tscr = mfspr(SPRN_TSCR);
> > + sprs.worc = mfspr(SPRN_WORC);
> > +
> > + sprs.sdr1 = mfspr(SPRN_SDR1);
> > + sprs.rpr = mfspr(SPRN_RPR);
> > + sprs.amor = mfspr(SPRN_AMOR);
> > +
> > + sprs.lpcr = mfspr(SPRN_LPCR);
> > + if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
> > + sprs.hfscr = mfspr(SPRN_HFSCR);
> > + sprs.fscr = mfspr(SPRN_FSCR);
> > + }
> > + sprs.purr = mfspr(SPRN_PURR);
> > + sprs.spurr = mfspr(SPRN_SPURR);
> > + sprs.dscr = mfspr(SPRN_DSCR);
> > + sprs.wort = mfspr(SPRN_WORT);
> > +
> > + sprs_saved = true;
> > +
> > + /*
> > + * Increment winkle counter and set all winkle bits if
> > + * all threads are winkling. This allows wakeup side to
> > + * distinguish between fast sleep and winkle state
> > + * loss. Fast sleep still has to resync the timebase so
> > + * this may not be a really big win.
> > + */
> > + *state += 1 << PNV_CORE_IDLE_WINKLE_COUNT_SHIFT;
> > + if ((*state & PNV_CORE_IDLE_WINKLE_COUNT_BITS) >>
> > PNV_CORE_IDLE_WINKLE_COUNT_SHIFT == threads_per_core)
> > + *state |= PNV_CORE_IDLE_THREAD_WINKLE_BITS;
> > + WARN_ON((*state & PNV_CORE_IDLE_WINKLE_COUNT_BITS) ==
> > 0);
> > + }
> > +
> > + atomic_unlock_thread_idle();
> > + }
> > +
>
> Could we add the following for debug purposes. We are already dumping
> thread_idle_state in xmon.
>
> paca->thread_idle_state = type;
>
> > + srr1 = isa206_idle_insn_mayloss(type);
>
> And the following:
> paca->thread_idle_state = PNV_THREAD_RUNNING;
Yes I'll add that.
>
> Apart from debugging purpose, IIRC, on some versions of POWER8,
> SRR1[46:47] wasn't being updated to 0b00 when we get an xscom SRESET
> while in running state. Thus, the only way to distinguish whether we
> entered 0x100 is due to a nap/fastsleep/winkle wakeup or due to an NMI
> caused when the processor wasn't in idle state was
> paca->thread_idle_state.
We don't actually do anything with that today, do we? Is that one
of the reasons we don't use xscom SRESET on POWER8?
>
> > +
> > + WARN_ON_ONCE(!srr1);
> > + WARN_ON_ONCE(mfmsr() & (MSR_IR|MSR_DR));
> > +
> > + if (unlikely((srr1 & SRR1_WAKEMASK_P8) == SRR1_WAKEHMI))
> [..snip..]
>
> > +static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
> > +{
> > + int cpu = raw_smp_processor_id();
> > + int first = cpu_first_thread_sibling(cpu);
> > + unsigned long *state = &paca_ptrs[first]->idle_state;
> > + unsigned long srr1;
> > + unsigned long mmcr0 = 0;
> > + struct p9_sprs sprs;
> > + bool sprs_saved = false;
> > +
> > + memset(&sprs, 0, sizeof(sprs));
> > +
> > + if (!(psscr & (PSSCR_EC|PSSCR_ESL))) {
> > + BUG_ON(!mmu_on);
> > +
> > + /*
> > + * Wake synchronously. SRESET via xscom may still cause
> > + * a 0x100 powersave wakeup with SRR1 reason!
> > + */
> > + srr1 = isa3_idle_stop_noloss(psscr);
> > + if (likely(!srr1))
> > + return 0;
> > +
>
> We come here if if we were woken up from a ESL=0 stop by a xscom
> SRESET. Where would the SRESET be handled ?
In irq_set_pending_from_srr1(), the same as EC=1 states.
>
> > + /*
> > + * Registers not saved, can't recover!
> > + * This would be a hardware bug
> > + */
> > + BUG_ON((srr1 & SRR1_WAKESTATE) != SRR1_WS_NOLOSS);
> > +
> > + goto out;
> > + }
> > +
>
>
> The patch looks good otherwise, especially the idle_book3s.S :-)
>
> Reviewed-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
Thank you for all the reviews
Thanks,
Nick
