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Subject[PATCH v5 03/18] perf: add Intel X86 LBR sharing logic
Date
The Intel LBR on some recent processor is capable
of filtering branches by type. The filter is configurable
via the LBR_SELECT MSR register.

There are limitation on how this register can be used.

On Nehalem/Westmere, the LBR_SELECT is shared by the two HT threads
when HT is on. It is private to each core when HT is off.

On SandyBridge, the LBR_SELECT register is private to each thread
when HT is on. It is private to each core when HT is off.

The kernel must manage the sharing of LBR_SELECT. It allows
multiple users on the same logical CPU to use LBR_SELECT as
long as they program it with the same value. Across sibling
CPUs (HT threads), the same restriction applies on NHM/WSM.

This patch implements this sharing logic by leveraging the
mechanism put in place for managing the offcore_response
shared MSR.

We modify __intel_shared_reg_get_constraints() to cause
x86_get_event_constraint() to be called because LBR may
be associated with events that may be counter constrained.

Signed-off-by: Stephane Eranian <eranian@google.com>
---
arch/x86/kernel/cpu/perf_event.c | 4 ++
arch/x86/kernel/cpu/perf_event.h | 4 ++
arch/x86/kernel/cpu/perf_event_intel.c | 70 ++++++++++++++++++++------------
3 files changed, 52 insertions(+), 26 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index f8bddb5..3779313 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -426,6 +426,10 @@ static int __x86_pmu_event_init(struct perf_event *event)
/* mark unused */
event->hw.extra_reg.idx = EXTRA_REG_NONE;

+ /* mark not used */
+ event->hw.extra_reg.idx = EXTRA_REG_NONE;
+ event->hw.branch_reg.idx = EXTRA_REG_NONE;
+
return x86_pmu.hw_config(event);
}

diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index 513d617..4535ada 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -33,6 +33,7 @@ enum extra_reg_type {

EXTRA_REG_RSP_0 = 0, /* offcore_response_0 */
EXTRA_REG_RSP_1 = 1, /* offcore_response_1 */
+ EXTRA_REG_LBR = 2, /* lbr_select */

EXTRA_REG_MAX /* number of entries needed */
};
@@ -130,6 +131,7 @@ struct cpu_hw_events {
void *lbr_context;
struct perf_branch_stack lbr_stack;
struct perf_branch_entry lbr_entries[MAX_LBR_ENTRIES];
+ struct er_account *lbr_sel;

/*
* Intel host/guest exclude bits
@@ -340,6 +342,8 @@ struct x86_pmu {
*/
unsigned long lbr_tos, lbr_from, lbr_to; /* MSR base regs */
int lbr_nr; /* hardware stack size */
+ u64 lbr_sel_mask; /* LBR_SELECT valid bits */
+ const int *lbr_sel_map; /* lbr_select mappings */

/*
* Extra registers for events
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 3bd37bd..97f7bb5 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1123,17 +1123,17 @@ static bool intel_try_alt_er(struct perf_event *event, int orig_idx)
*/
static struct event_constraint *
__intel_shared_reg_get_constraints(struct cpu_hw_events *cpuc,
- struct perf_event *event)
+ struct perf_event *event,
+ struct hw_perf_event_extra *reg)
{
struct event_constraint *c = &emptyconstraint;
- struct hw_perf_event_extra *reg = &event->hw.extra_reg;
struct er_account *era;
unsigned long flags;
int orig_idx = reg->idx;

/* already allocated shared msr */
if (reg->alloc)
- return &unconstrained;
+ return NULL; /* call x86_get_event_constraint() */

again:
era = &cpuc->shared_regs->regs[reg->idx];
@@ -1156,14 +1156,10 @@ __intel_shared_reg_get_constraints(struct cpu_hw_events *cpuc,
reg->alloc = 1;

/*
- * All events using extra_reg are unconstrained.
- * Avoids calling x86_get_event_constraints()
- *
- * Must revisit if extra_reg controlling events
- * ever have constraints. Worst case we go through
- * the regular event constraint table.
+ * need to call x86_get_event_constraint()
+ * to check if associated event has constraints
*/
- c = &unconstrained;
+ c = NULL;
} else if (intel_try_alt_er(event, orig_idx)) {
raw_spin_unlock_irqrestore(&era->lock, flags);
goto again;
@@ -1200,11 +1196,23 @@ static struct event_constraint *
intel_shared_regs_constraints(struct cpu_hw_events *cpuc,
struct perf_event *event)
{
- struct event_constraint *c = NULL;
-
- if (event->hw.extra_reg.idx != EXTRA_REG_NONE)
- c = __intel_shared_reg_get_constraints(cpuc, event);
-
+ struct event_constraint *c = NULL, *d;
+ struct hw_perf_event_extra *xreg, *breg;
+
+ xreg = &event->hw.extra_reg;
+ if (xreg->idx != EXTRA_REG_NONE) {
+ c = __intel_shared_reg_get_constraints(cpuc, event, xreg);
+ if (c == &emptyconstraint)
+ return c;
+ }
+ breg = &event->hw.branch_reg;
+ if (breg->idx != EXTRA_REG_NONE) {
+ d = __intel_shared_reg_get_constraints(cpuc, event, breg);
+ if (d == &emptyconstraint) {
+ __intel_shared_reg_put_constraints(cpuc, xreg);
+ c = d;
+ }
+ }
return c;
}

@@ -1252,6 +1260,10 @@ intel_put_shared_regs_event_constraints(struct cpu_hw_events *cpuc,
reg = &event->hw.extra_reg;
if (reg->idx != EXTRA_REG_NONE)
__intel_shared_reg_put_constraints(cpuc, reg);
+
+ reg = &event->hw.branch_reg;
+ if (reg->idx != EXTRA_REG_NONE)
+ __intel_shared_reg_put_constraints(cpuc, reg);
}

static void intel_put_event_constraints(struct cpu_hw_events *cpuc,
@@ -1431,7 +1443,7 @@ static int intel_pmu_cpu_prepare(int cpu)
{
struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);

- if (!x86_pmu.extra_regs)
+ if (!(x86_pmu.extra_regs || x86_pmu.lbr_sel_map))
return NOTIFY_OK;

cpuc->shared_regs = allocate_shared_regs(cpu);
@@ -1453,22 +1465,28 @@ static void intel_pmu_cpu_starting(int cpu)
*/
intel_pmu_lbr_reset();

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

- for_each_cpu(i, topology_thread_cpumask(cpu)) {
- struct intel_shared_regs *pc;
+ if (!(x86_pmu.er_flags & ERF_NO_HT_SHARING)) {
+ for_each_cpu(i, topology_thread_cpumask(cpu)) {
+ struct intel_shared_regs *pc;

- pc = per_cpu(cpu_hw_events, i).shared_regs;
- if (pc && pc->core_id == core_id) {
- cpuc->kfree_on_online = cpuc->shared_regs;
- cpuc->shared_regs = pc;
- break;
+ pc = per_cpu(cpu_hw_events, i).shared_regs;
+ if (pc && pc->core_id == core_id) {
+ cpuc->kfree_on_online = cpuc->shared_regs;
+ cpuc->shared_regs = pc;
+ break;
+ }
}
+ cpuc->shared_regs->core_id = core_id;
+ cpuc->shared_regs->refcnt++;
}

- cpuc->shared_regs->core_id = core_id;
- cpuc->shared_regs->refcnt++;
+ if (x86_pmu.lbr_sel_map)
+ cpuc->lbr_sel = &cpuc->shared_regs->regs[EXTRA_REG_LBR];
}

static void intel_pmu_cpu_dying(int cpu)
--
1.7.4.1


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