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SubjectRe: [PATCH 0/3] perf_events: update extra shared registers management
Peter,

The following revised patch seems to work for me on top of my
series (well, the modified one with irqsave):

$ syst_count -c 0 -p -e offcore_response_0:dmnd_data_rd:k,\
offcore_response_0:dmnd_rfo:u,\
offcore_response_0:dmnd_rfo:k,\
offcore_response_0:dmnd_data_rd:u

CPU0 G0 478 offcore_response_0:dmnd_data_rd:k (scaling 0.00%, ena=997285681, run=997285681)
CPU0 G0 163 offcore_response_0:dmnd_rfo (scaling 0.00%, ena=997285681, run=997285681)
CPU0 G0 163 offcore_response_0:dmnd_rfo (scaling 0.00%, ena=997285681, run=997285681)
CPU0 G0 0 offcore_response_0:dmnd_data_rd:u (scaling 0.00%, ena=997285681, run=997285681)

Subject: perf, intel: Try alternative OFFCORE encoding
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Mon May 23 11:08:15 CEST 2011

Since the OFFCORE registers are fully symmetric, try the other when the
speficied one is already taken.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Stephane Eranian <eranian@google.com>
---

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index d6ad9c2..59e7004 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -326,9 +326,12 @@ struct x86_pmu {
* Extra registers for events
*/
struct extra_reg *extra_regs;
- bool regs_no_ht_sharing;
+ unsigned int er_flags;
};

+#define ERF_NO_HT_SHARING 1
+#define ERF_HAS_RSP_1 2
+
static struct x86_pmu x86_pmu __read_mostly;

static DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = {
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 9904205..9d1dd2b 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1019,6 +1019,35 @@ intel_bts_constraints(struct perf_event *event)
return NULL;
}

+static bool intel_try_alt_er(struct perf_event *event, int idx)
+{
+ if (!(x86_pmu.er_flags & ERF_HAS_RSP_1))
+ return false;
+
+ /*
+ * there are at most 2 offcore_response registers
+ * if we come here for the secodn time, then it
+ * means we have exhausted all possible alternatives
+ */
+ if (event->hw.extra_reg.alt_cnt == 1)
+ return false;
+
+ if (event->hw.extra_reg.idx == EXTRA_REG_RSP_0) {
+ event->hw.config &= ~INTEL_ARCH_EVENT_MASK;
+ event->hw.config |= 0x01bb;
+ event->hw.extra_reg.idx = EXTRA_REG_RSP_1;
+ event->hw.extra_reg.reg = MSR_OFFCORE_RSP_1;
+ } else if (event->hw.extra_reg.idx == EXTRA_REG_RSP_1) {
+ event->hw.config &= ~INTEL_ARCH_EVENT_MASK;
+ event->hw.config |= 0x01b7;
+ event->hw.extra_reg.idx = EXTRA_REG_RSP_0;
+ event->hw.extra_reg.reg = MSR_OFFCORE_RSP_0;
+ }
+ event->hw.extra_reg.alt_cnt++;
+
+ return true;
+}
+
/*
* manage allocation of shared extra msr for certain events
*
@@ -1028,9 +1057,10 @@ intel_bts_constraints(struct perf_event *event)
*/
static struct event_constraint *
__intel_shared_reg_get_constraints(struct cpu_hw_events *cpuc,
- struct hw_perf_event_extra *reg)
+ struct perf_event *event)
{
struct event_constraint *c = &emptyconstraint;
+ struct hw_perf_event_extra *reg = &event->hw.extra_reg;
struct er_account *era;
unsigned long flags;

@@ -1038,6 +1068,9 @@ __intel_shared_reg_get_constraints(struct cpu_hw_events *cpuc,
if (reg->alloc)
return &unconstrained;

+ /* reset alternate indexes tried */
+ reg->alt_cnt = 0;
+again:
era = &cpuc->shared_regs->regs[reg->idx];
/*
* we use spin_lock_irqsave() to avoid lockdep issues when
@@ -1066,6 +1099,9 @@ __intel_shared_reg_get_constraints(struct cpu_hw_events *cpuc,
* the regular event constraint table.
*/
c = &unconstrained;
+ } else if (intel_try_alt_er(event, reg->idx)) {
+ raw_spin_unlock_irqrestore(&era->lock, flags);
+ goto again;
}
raw_spin_unlock_irqrestore(&era->lock, flags);

@@ -1100,11 +1136,9 @@ intel_shared_regs_constraints(struct cpu_hw_events *cpuc,
struct perf_event *event)
{
struct event_constraint *c = NULL;
- struct hw_perf_event_extra *xreg;

- xreg = &event->hw.extra_reg;
- if (xreg->idx != EXTRA_REG_NONE)
- c = __intel_shared_reg_get_constraints(cpuc, xreg);
+ if (event->hw.extra_reg.idx != EXTRA_REG_NONE)
+ c = __intel_shared_reg_get_constraints(cpuc, event);
return c;
}

@@ -1265,7 +1299,7 @@ static void intel_pmu_cpu_starting(int cpu)
*/
intel_pmu_lbr_reset();

- if (!cpuc->shared_regs || x86_pmu.regs_no_ht_sharing)
+ if (!cpuc->shared_regs || (x86_pmu.er_flags & ERF_NO_HT_SHARING))
return;

for_each_cpu(i, topology_thread_cpumask(cpu)) {
@@ -1490,6 +1524,7 @@ static __init int intel_pmu_init(void)
x86_pmu.enable_all = intel_pmu_nhm_enable_all;
x86_pmu.pebs_constraints = intel_westmere_pebs_event_constraints;
x86_pmu.extra_regs = intel_westmere_extra_regs;
+ x86_pmu.er_flags |= ERF_HAS_RSP_1;

/* UOPS_ISSUED.STALLED_CYCLES */
intel_perfmon_event_map[PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = 0x180010e;
@@ -1509,7 +1544,8 @@ static __init int intel_pmu_init(void)
x86_pmu.pebs_constraints = intel_snb_pebs_events;
x86_pmu.extra_regs = intel_snb_extra_regs;
/* all extra regs are per-cpu when HT is on */
- x86_pmu.regs_no_ht_sharing = true;
+ x86_pmu.er_flags |= ERF_HAS_RSP_1;
+ x86_pmu.er_flags |= ERF_NO_HT_SHARING;

/* UOPS_ISSUED.ANY,c=1,i=1 to count stall cycles */
intel_perfmon_event_map[PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = 0x180010e;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 941f40d..1671cd8 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -544,6 +544,7 @@ struct hw_perf_event_extra {
unsigned int reg; /* register address or index */
int alloc; /* extra register already allocated */
int idx; /* index in shared_regs->regs[] */
+ int alt_cnt;/* number of alternate indexes tried */
};

/**

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