perf_counter: powerpc: allow use of limited-function counters

POWER5+ and POWER6 have two hardware counters with limited functionality:
PMC5 counts instructions completed in run state and PMC6 counts cycles
in run state.  (Run state is the state when a hardware RUN bit is 1;
the idle task clears RUN while waiting for work to do and sets it when
there is work to do.)

These counters can't be written to by the kernel, can't generate
interrupts, and don't obey the freeze conditions.  That means we can
only use them for per-task counters (where we know we'll always be in
run state; we can't put a per-task counter on an idle task), and only
if we don't want interrupts and we do want to count in all processor
modes.

Obviously some counters can't go on a limited hardware counter, but there
are also situations where we can only put a counter on a limited hardware
counter - if there are already counters on that exclude some processor
modes and we want to put on a per-task cycle or instruction counter that
doesn't exclude any processor mode, it could go on if it can use a
limited hardware counter.

To keep track of these constraints, this adds a flags argument to the
processor-specific get_alternatives() functions, with three bits defined:
one to say that we can accept alternative event codes that go on limited
counters, one to say we only want alternatives on limited counters, and
one to say that this is a per-task counter and therefore events that are
gated by run state are equivalent to those that aren't (e.g. a "cycles"
event is equivalent to a "cycles in run state" event).  These flags
are computed for each counter and stored in the counter->hw.counter_base
field (slightly wonky name for what it does, but it was an existing
unused field).

Since the limited counters don't freeze when we freeze the other counters,
we need some special handling to avoid getting skew between things counted
on the limited counters and those counted on normal counters.  To minimize
this skew, if we are using any limited counters, we read PMC5 and PMC6
immediately after setting and clearing the freeze bit.  This is done in
a single asm in the new write_mmcr0() function.

The code here is specific to PMC5 and PMC6 being the limited hardware
counters.  Being more general (e.g. having a bitmap of limited hardware
counter numbers) would have meant more complex code to read the limited
counters when freezing and unfreezing the normal counters, with
conditional branches, which would have increased the skew.  Since it
isn't necessary for the code to be more general at this stage, it isn't.

This also extends the back-ends for POWER5+ and POWER6 to be able to
handle up to 6 counters rather than the 4 they previously handled.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Robert Richter <robert.richter@amd.com>
LKML-Reference: <18936.19035.163066.892208@cargo.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 262 insertions, 35 deletions

diff --git a/arch/powerpc/kernel/perf_counter.c b/arch/powerpc/kernel/perf_counter.c
index d9bbe5efc649..15cdc8e67229 100644
--- a/arch/powerpc/kernel/perf_counter.c
+++ b/arch/powerpc/kernel/perf_counter.c
@@ -23,10 +23,14 @@ struct cpu_hw_counters {
         int n_percpu;
         int disabled;
         int n_added;
+        int n_limited;
+        u8  pmcs_enabled;
         struct perf_counter *counter[MAX_HWCOUNTERS];
         unsigned int events[MAX_HWCOUNTERS];
+        unsigned int flags[MAX_HWCOUNTERS];
         u64 mmcr[3];
-        u8 pmcs_enabled;
+        struct perf_counter *limited_counter[MAX_LIMITED_HWCOUNTERS];
+        u8  limited_hwidx[MAX_LIMITED_HWCOUNTERS];
 };
 DEFINE_PER_CPU(struct cpu_hw_counters, cpu_hw_counters);
 
@@ -127,7 +131,8 @@ static void write_pmc(int idx, unsigned long val)
  * and see if any combination of alternative codes is feasible.
  * The feasible set is returned in event[].
  */
-static int power_check_constraints(unsigned int event[], int n_ev)
+static int power_check_constraints(unsigned int event[], unsigned int cflags[],
+                                   int n_ev)
 {
         u64 mask, value, nv;
         unsigned int alternatives[MAX_HWCOUNTERS][MAX_EVENT_ALTERNATIVES];
@@ -144,11 +149,15 @@ static int power_check_constraints(unsigned int event[], int n_ev)
 
         /* First see if the events will go on as-is */
         for (i = 0; i < n_ev; ++i) {
-                alternatives[i][0] = event[i];
+                if ((cflags[i] & PPMU_LIMITED_PMC_REQD)
+                    && !ppmu->limited_pmc_event(event[i])) {
+                        ppmu->get_alternatives(event[i], cflags[i],
+                                               alternatives[i]);
+                        event[i] = alternatives[i][0];
+                }
                 if (ppmu->get_constraint(event[i], &amasks[i][0],
                                          &avalues[i][0]))
                         return -1;
-                choice[i] = 0;
         }
         value = mask = 0;
         for (i = 0; i < n_ev; ++i) {
@@ -166,7 +175,9 @@ static int power_check_constraints(unsigned int event[], int n_ev)
         if (!ppmu->get_alternatives)
                 return -1;
         for (i = 0; i < n_ev; ++i) {
-                n_alt[i] = ppmu->get_alternatives(event[i], alternatives[i]);
+                choice[i] = 0;
+                n_alt[i] = ppmu->get_alternatives(event[i], cflags[i],
+                                                  alternatives[i]);
                 for (j = 1; j < n_alt[i]; ++j)
                         ppmu->get_constraint(alternatives[i][j],
                                              &amasks[i][j], &avalues[i][j]);
@@ -231,28 +242,41 @@ static int power_check_constraints(unsigned int event[], int n_ev)
  * exclude_{user,kernel,hv} with each other and any previously
  * added counters.
  */
-static int check_excludes(struct perf_counter **ctrs, int n_prev, int n_new)
+static int check_excludes(struct perf_counter **ctrs, unsigned int cflags[],
+                          int n_prev, int n_new)
 {
-        int eu, ek, eh;
-        int i, n;
+        int eu = 0, ek = 0, eh = 0;
+        int i, n, first;
         struct perf_counter *counter;
 
         n = n_prev + n_new;
         if (n <= 1)
                 return 0;
 
-        eu = ctrs[0]->hw_event.exclude_user;
-        ek = ctrs[0]->hw_event.exclude_kernel;
-        eh = ctrs[0]->hw_event.exclude_hv;
-        if (n_prev == 0)
-                n_prev = 1;
-        for (i = n_prev; i < n; ++i) {
+        first = 1;
+        for (i = 0; i < n; ++i) {
+                if (cflags[i] & PPMU_LIMITED_PMC_OK) {
+                        cflags[i] &= ~PPMU_LIMITED_PMC_REQD;
+                        continue;
+                }
                 counter = ctrs[i];
-                if (counter->hw_event.exclude_user != eu ||
-                    counter->hw_event.exclude_kernel != ek ||
-                    counter->hw_event.exclude_hv != eh)
+                if (first) {
+                        eu = counter->hw_event.exclude_user;
+                        ek = counter->hw_event.exclude_kernel;
+                        eh = counter->hw_event.exclude_hv;
+                        first = 0;
+                } else if (counter->hw_event.exclude_user != eu ||
+                           counter->hw_event.exclude_kernel != ek ||
+                           counter->hw_event.exclude_hv != eh) {
                         return -EAGAIN;
+                }
         }
+
+        if (eu || ek || eh)
+                for (i = 0; i < n; ++i)
+                        if (cflags[i] & PPMU_LIMITED_PMC_OK)
+                                cflags[i] |= PPMU_LIMITED_PMC_REQD;
+
         return 0;
 }
 
@@ -280,6 +304,85 @@ static void power_pmu_read(struct perf_counter *counter)
 }
 
 /*
+ * On some machines, PMC5 and PMC6 can't be written, don't respect
+ * the freeze conditions, and don't generate interrupts.  This tells
+ * us if `counter' is using such a PMC.
+ */
+static int is_limited_pmc(int pmcnum)
+{
+        return ppmu->limited_pmc5_6 && (pmcnum == 5 || pmcnum == 6);
+}
+
+static void freeze_limited_counters(struct cpu_hw_counters *cpuhw,
+                                    unsigned long pmc5, unsigned long pmc6)
+{
+        struct perf_counter *counter;
+        u64 val, prev, delta;
+        int i;
+
+        for (i = 0; i < cpuhw->n_limited; ++i) {
+                counter = cpuhw->limited_counter[i];
+                if (!counter->hw.idx)
+                        continue;
+                val = (counter->hw.idx == 5) ? pmc5 : pmc6;
+                prev = atomic64_read(&counter->hw.prev_count);
+                counter->hw.idx = 0;
+                delta = (val - prev) & 0xfffffffful;
+                atomic64_add(delta, &counter->count);
+        }
+}
+
+static void thaw_limited_counters(struct cpu_hw_counters *cpuhw,
+                                  unsigned long pmc5, unsigned long pmc6)
+{
+        struct perf_counter *counter;
+        u64 val;
+        int i;
+
+        for (i = 0; i < cpuhw->n_limited; ++i) {
+                counter = cpuhw->limited_counter[i];
+                counter->hw.idx = cpuhw->limited_hwidx[i];
+                val = (counter->hw.idx == 5) ? pmc5 : pmc6;
+                atomic64_set(&counter->hw.prev_count, val);
+                perf_counter_update_userpage(counter);
+        }
+}
+
+/*
+ * Since limited counters don't respect the freeze conditions, we
+ * have to read them immediately after freezing or unfreezing the
+ * other counters.  We try to keep the values from the limited
+ * counters as consistent as possible by keeping the delay (in
+ * cycles and instructions) between freezing/unfreezing and reading
+ * the limited counters as small and consistent as possible.
+ * Therefore, if any limited counters are in use, we read them
+ * both, and always in the same order, to minimize variability,
+ * and do it inside the same asm that writes MMCR0.
+ */
+static void write_mmcr0(struct cpu_hw_counters *cpuhw, unsigned long mmcr0)
+{
+        unsigned long pmc5, pmc6;
+
+        if (!cpuhw->n_limited) {
+                mtspr(SPRN_MMCR0, mmcr0);
+                return;
+        }
+
+        /*
+         * Write MMCR0, then read PMC5 and PMC6 immediately.
+         */
+        asm volatile("mtspr %3,%2; mfspr %0,%4; mfspr %1,%5"
+                     : "=&r" (pmc5), "=&r" (pmc6)
+                     : "r" (mmcr0), "i" (SPRN_MMCR0),
+                       "i" (SPRN_PMC5), "i" (SPRN_PMC6));
+
+        if (mmcr0 & MMCR0_FC)
+                freeze_limited_counters(cpuhw, pmc5, pmc6);
+        else
+                thaw_limited_counters(cpuhw, pmc5, pmc6);
+}
+
+/*
  * Disable all counters to prevent PMU interrupts and to allow
  * counters to be added or removed.
  */
@@ -321,7 +424,7 @@ u64 hw_perf_save_disable(void)
                  * executed and the PMU has frozen the counters
                  * before we return.
                  */
-                mtspr(SPRN_MMCR0, mfspr(SPRN_MMCR0) | MMCR0_FC);
+                write_mmcr0(cpuhw, mfspr(SPRN_MMCR0) | MMCR0_FC);
                 mb();
         }
         local_irq_restore(flags);
@@ -342,6 +445,8 @@ void hw_perf_restore(u64 disable)
         unsigned long val;
         s64 left;
         unsigned int hwc_index[MAX_HWCOUNTERS];
+        int n_lim;
+        int idx;
 
         if (disable)
                 return;
@@ -414,10 +519,18 @@ void hw_perf_restore(u64 disable)
         /*
          * Initialize the PMCs for all the new and moved counters.
          */
+        cpuhw->n_limited = n_lim = 0;
         for (i = 0; i < cpuhw->n_counters; ++i) {
                 counter = cpuhw->counter[i];
                 if (counter->hw.idx)
                         continue;
+                idx = hwc_index[i] + 1;
+                if (is_limited_pmc(idx)) {
+                        cpuhw->limited_counter[n_lim] = counter;
+                        cpuhw->limited_hwidx[n_lim] = idx;
+                        ++n_lim;
+                        continue;
+                }
                 val = 0;
                 if (counter->hw_event.irq_period) {
                         left = atomic64_read(&counter->hw.period_left);
@@ -425,15 +538,16 @@ void hw_perf_restore(u64 disable)
                                 val = 0x80000000L - left;
                 }
                 atomic64_set(&counter->hw.prev_count, val);
-                counter->hw.idx = hwc_index[i] + 1;
-                write_pmc(counter->hw.idx, val);
+                counter->hw.idx = idx;
+                write_pmc(idx, val);
                 perf_counter_update_userpage(counter);
         }
+        cpuhw->n_limited = n_lim;
         cpuhw->mmcr[0] |= MMCR0_PMXE | MMCR0_FCECE;
 
  out_enable:
         mb();
-        mtspr(SPRN_MMCR0, cpuhw->mmcr[0]);
+        write_mmcr0(cpuhw, cpuhw->mmcr[0]);
 
         /*
          * Enable instruction sampling if necessary
@@ -448,7 +562,8 @@ void hw_perf_restore(u64 disable)
 }
 
 static int collect_events(struct perf_counter *group, int max_count,
-                          struct perf_counter *ctrs[], unsigned int *events)
+                          struct perf_counter *ctrs[], unsigned int *events,
+                          unsigned int *flags)
 {
         int n = 0;
         struct perf_counter *counter;
@@ -457,6 +572,7 @@ static int collect_events(struct perf_counter *group, int max_count,
                 if (n >= max_count)
                         return -1;
                 ctrs[n] = group;
+                flags[n] = group->hw.counter_base;
                 events[n++] = group->hw.config;
         }
         list_for_each_entry(counter, &group->sibling_list, list_entry) {
@@ -465,6 +581,7 @@ static int collect_events(struct perf_counter *group, int max_count,
                         if (n >= max_count)
                                 return -1;
                         ctrs[n] = counter;
+                        flags[n] = counter->hw.counter_base;
                         events[n++] = counter->hw.config;
                 }
         }
@@ -497,12 +614,14 @@ int hw_perf_group_sched_in(struct perf_counter *group_leader,
         cpuhw = &__get_cpu_var(cpu_hw_counters);
         n0 = cpuhw->n_counters;
         n = collect_events(group_leader, ppmu->n_counter - n0,
-                           &cpuhw->counter[n0], &cpuhw->events[n0]);
+                           &cpuhw->counter[n0], &cpuhw->events[n0],
+                           &cpuhw->flags[n0]);
         if (n < 0)
                 return -EAGAIN;
-        if (check_excludes(cpuhw->counter, n0, n))
+        if (check_excludes(cpuhw->counter, cpuhw->flags, n0, n))
                 return -EAGAIN;
-        if (power_check_constraints(cpuhw->events, n + n0))
+        i = power_check_constraints(cpuhw->events, cpuhw->flags, n + n0);
+        if (i < 0)
                 return -EAGAIN;
         cpuhw->n_counters = n0 + n;
         cpuhw->n_added += n;
@@ -554,9 +673,10 @@ static int power_pmu_enable(struct perf_counter *counter)
                 goto out;
         cpuhw->counter[n0] = counter;
         cpuhw->events[n0] = counter->hw.config;
-        if (check_excludes(cpuhw->counter, n0, 1))
+        cpuhw->flags[n0] = counter->hw.counter_base;
+        if (check_excludes(cpuhw->counter, cpuhw->flags, n0, 1))
                 goto out;
-        if (power_check_constraints(cpuhw->events, n0 + 1))
+        if (power_check_constraints(cpuhw->events, cpuhw->flags, n0 + 1))
                 goto out;
 
         counter->hw.config = cpuhw->events[n0];
@@ -592,12 +712,24 @@ static void power_pmu_disable(struct perf_counter *counter)
                                 cpuhw->counter[i-1] = cpuhw->counter[i];
                         --cpuhw->n_counters;
                         ppmu->disable_pmc(counter->hw.idx - 1, cpuhw->mmcr);
-                        write_pmc(counter->hw.idx, 0);
-                        counter->hw.idx = 0;
+                        if (counter->hw.idx) {
+                                write_pmc(counter->hw.idx, 0);
+                                counter->hw.idx = 0;
+                        }
                         perf_counter_update_userpage(counter);
                         break;
                 }
         }
+        for (i = 0; i < cpuhw->n_limited; ++i)
+                if (counter == cpuhw->limited_counter[i])
+                        break;
+        if (i < cpuhw->n_limited) {
+                while (++i < cpuhw->n_limited) {
+                        cpuhw->limited_counter[i-1] = cpuhw->limited_counter[i];
+                        cpuhw->limited_hwidx[i-1] = cpuhw->limited_hwidx[i];
+                }
+                --cpuhw->n_limited;
+        }
         if (cpuhw->n_counters == 0) {
                 /* disable exceptions if no counters are running */
                 cpuhw->mmcr[0] &= ~(MMCR0_PMXE | MMCR0_FCECE);
@@ -613,6 +745,61 @@ struct pmu power_pmu = {
         .read           = power_pmu_read,
 };
 
+/*
+ * Return 1 if we might be able to put counter on a limited PMC,
+ * or 0 if not.
+ * A counter can only go on a limited PMC if it counts something
+ * that a limited PMC can count, doesn't require interrupts, and
+ * doesn't exclude any processor mode.
+ */
+static int can_go_on_limited_pmc(struct perf_counter *counter, unsigned int ev,
+                                 unsigned int flags)
+{
+        int n;
+        unsigned int alt[MAX_EVENT_ALTERNATIVES];
+
+        if (counter->hw_event.exclude_user
+            || counter->hw_event.exclude_kernel
+            || counter->hw_event.exclude_hv
+            || counter->hw_event.irq_period)
+                return 0;
+
+        if (ppmu->limited_pmc_event(ev))
+                return 1;
+
+        /*
+         * The requested event isn't on a limited PMC already;
+         * see if any alternative code goes on a limited PMC.
+         */
+        if (!ppmu->get_alternatives)
+                return 0;
+
+        flags |= PPMU_LIMITED_PMC_OK | PPMU_LIMITED_PMC_REQD;
+        n = ppmu->get_alternatives(ev, flags, alt);
+        if (n)
+                return alt[0];
+
+        return 0;
+}
+
+/*
+ * Find an alternative event that goes on a normal PMC, if possible,
+ * and return the event code, or 0 if there is no such alternative.
+ * (Note: event code 0 is "don't count" on all machines.)
+ */
+static unsigned long normal_pmc_alternative(unsigned long ev,
+                                            unsigned long flags)
+{
+        unsigned int alt[MAX_EVENT_ALTERNATIVES];
+        int n;
+
+        flags &= ~(PPMU_LIMITED_PMC_OK | PPMU_LIMITED_PMC_REQD);
+        n = ppmu->get_alternatives(ev, flags, alt);
+        if (!n)
+                return 0;
+        return alt[0];
+}
+
 /* Number of perf_counters counting hardware events */
 static atomic_t num_counters;
 /* Used to avoid races in calling reserve/release_pmc_hardware */
@@ -633,9 +820,10 @@ static void hw_perf_counter_destroy(struct perf_counter *counter)
 
 const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
 {
-        unsigned long ev;
+        unsigned long ev, flags;
         struct perf_counter *ctrs[MAX_HWCOUNTERS];
         unsigned int events[MAX_HWCOUNTERS];
+        unsigned int cflags[MAX_HWCOUNTERS];
         int n;
         int err;
 
@@ -661,7 +849,36 @@ const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
          */
         if (!firmware_has_feature(FW_FEATURE_LPAR))
                 counter->hw_event.exclude_hv = 0;
-        
+
+        /*
+         * If this is a per-task counter, then we can use
+         * PM_RUN_* events interchangeably with their non RUN_*
+         * equivalents, e.g. PM_RUN_CYC instead of PM_CYC.
+         * XXX we should check if the task is an idle task.
+         */
+        flags = 0;
+        if (counter->ctx->task)
+                flags |= PPMU_ONLY_COUNT_RUN;
+
+        /*
+         * If this machine has limited counters, check whether this
+         * event could go on a limited counter.
+         */
+        if (ppmu->limited_pmc5_6) {
+                if (can_go_on_limited_pmc(counter, ev, flags)) {
+                        flags |= PPMU_LIMITED_PMC_OK;
+                } else if (ppmu->limited_pmc_event(ev)) {
+                        /*
+                         * The requested event is on a limited PMC,
+                         * but we can't use a limited PMC; see if any
+                         * alternative goes on a normal PMC.
+                         */
+                        ev = normal_pmc_alternative(ev, flags);
+                        if (!ev)
+                                return ERR_PTR(-EINVAL);
+                }
+        }
+
         /*
          * If this is in a group, check if it can go on with all the
          * other hardware counters in the group.  We assume the counter
@@ -670,18 +887,20 @@ const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
         n = 0;
         if (counter->group_leader != counter) {
                 n = collect_events(counter->group_leader, ppmu->n_counter - 1,
-                                   ctrs, events);
+                                   ctrs, events, cflags);
                 if (n < 0)
                         return ERR_PTR(-EINVAL);
         }
         events[n] = ev;
         ctrs[n] = counter;
-        if (check_excludes(ctrs, n, 1))
+        cflags[n] = flags;
+        if (check_excludes(ctrs, cflags, n, 1))
                 return ERR_PTR(-EINVAL);
-        if (power_check_constraints(events, n + 1))
+        if (power_check_constraints(events, cflags, n + 1))
                 return ERR_PTR(-EINVAL);
 
         counter->hw.config = events[n];
+        counter->hw.counter_base = cflags[n];
         atomic64_set(&counter->hw.period_left, counter->hw_event.irq_period);
 
         /*
@@ -763,6 +982,10 @@ static void perf_counter_interrupt(struct pt_regs *regs)
         int found = 0;
         int nmi;
 
+        if (cpuhw->n_limited)
+                freeze_limited_counters(cpuhw, mfspr(SPRN_PMC5),
+                                        mfspr(SPRN_PMC6));
+
         /*
          * If interrupts were soft-disabled when this PMU interrupt
          * occurred, treat it as an NMI.
@@ -775,6 +998,8 @@ static void perf_counter_interrupt(struct pt_regs *regs)
 
         for (i = 0; i < cpuhw->n_counters; ++i) {
                 counter = cpuhw->counter[i];
+                if (is_limited_pmc(counter->hw.idx))
+                        continue;
                 val = read_pmc(counter->hw.idx);
                 if ((int)val < 0) {
                         /* counter has overflowed */
@@ -791,6 +1016,8 @@ static void perf_counter_interrupt(struct pt_regs *regs)
          */
         if (!found) {
                 for (i = 0; i < ppmu->n_counter; ++i) {
+                        if (is_limited_pmc(i + 1))
+                                continue;
                         val = read_pmc(i + 1);
                         if ((int)val < 0)
                                 write_pmc(i + 1, 0);
@@ -804,7 +1031,7 @@ static void perf_counter_interrupt(struct pt_regs *regs)
          * XXX might want to use MSR.PM to keep the counters frozen until
          * we get back out of this interrupt.
          */
-        mtspr(SPRN_MMCR0, cpuhw->mmcr[0]);
+        write_mmcr0(cpuhw, cpuhw->mmcr[0]);
 
         if (nmi)
                 nmi_exit();