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Subject[[PATCH v6 02/10] perf: Add a flags parameter to pmu txn interfaces
Date
Currently, the PMU interface allows reading only one counter at a time.
But some PMUs like the 24x7 counters in Power, support reading several
counters at once. To leveage this functionality, extend the transaction
interface to support a "transaction type".

The first type, PERF_PMU_TXN_ADD, refers to the existing transactions,
i.e. used to _schedule_ all the events on the PMU as a group. A second
transaction type, PERF_PMU_TXN_READ, will be used in a follow-on patch,
by the 24x7 counters to read several counters at once.

Extend the transaction interfaces to the PMU to accept a 'txn_flags'
parameter and use this parameter to ignore any transactions that are
not of type PERF_PMU_TXN_ADD.

Thanks to Peter Zijlstra for his input.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>

---
Changelog[v6]
- [Peter Zijlstra]
- Change txn_flags to unsigned int.
- In commit_txn() clear txn_flags independently for TXN_ADD
TXN_READ transactions (to reduce churn in a later patch).
- Drop local 'txn_flags' variable.
- Add WARN_ON_ONCE() around txn_flags.

Changelog[v4]
- [Peter Zijlstra] Fix an copy-paste error in power_pmu_cancel_txn().
- [Peter Zijlstra] Use __this_cpu_read() and __this_cpu_write().

Changelog[v3]
- [Peter Zijlstra] Ensure the nop_txn interfaces disable/enable
PMU only for TXN_ADD transactions.
- [Peter Zijlstra] Cache the flags parameter in ->start_txn() and
drop the flags parameter from ->commit_txn() and ->cancel_txn().
---
arch/powerpc/perf/core-book3s.c | 30 +++++++++++++++++++++++++++++-
arch/s390/kernel/perf_cpum_cf.c | 30 +++++++++++++++++++++++++++++-
arch/sparc/kernel/perf_event.c | 25 ++++++++++++++++++++++++-
arch/x86/kernel/cpu/perf_event.c | 32 +++++++++++++++++++++++++++++++-
arch/x86/kernel/cpu/perf_event.h | 1 +
include/linux/perf_event.h | 14 +++++++++++---
kernel/events/core.c | 31 ++++++++++++++++++++++++++++---
7 files changed, 153 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index d90893b..a9e9a39 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -49,6 +49,7 @@ struct cpu_hw_events {
unsigned long avalues[MAX_HWEVENTS][MAX_EVENT_ALTERNATIVES];

unsigned int group_flag;
+ unsigned int txn_flags;
int n_txn_start;

/* BHRB bits */
@@ -1586,11 +1587,21 @@ static void power_pmu_stop(struct perf_event *event, int ef_flags)
* Start group events scheduling transaction
* Set the flag to make pmu::enable() not perform the
* schedulability test, it will be performed at commit time
+ *
+ * We only support PERF_PMU_TXN_ADD transactions. Save the
+ * transaction flags but otherwise ignore non-PERF_PMU_TXN_ADD
+ * transactions.
*/
-static void power_pmu_start_txn(struct pmu *pmu)
+static void power_pmu_start_txn(struct pmu *pmu, unsigned int txn_flags)
{
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);

+ WARN_ON_ONCE(cpuhw->txn_flags); /* txn already in flight */
+
+ cpuhw->txn_flags = txn_flags;
+ if (txn_flags & ~PERF_PMU_TXN_ADD)
+ return;
+
perf_pmu_disable(pmu);
cpuhw->group_flag |= PERF_EVENT_TXN;
cpuhw->n_txn_start = cpuhw->n_events;
@@ -1604,6 +1615,14 @@ static void power_pmu_start_txn(struct pmu *pmu)
static void power_pmu_cancel_txn(struct pmu *pmu)
{
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
+ unsigned int txn_flags;
+
+ WARN_ON_ONCE(!cpuhw->txn_flags); /* no txn in flight */
+
+ txn_flags = cpuhw->txn_flags;
+ cpuhw->txn_flags = 0;
+ if (txn_flags & ~PERF_PMU_TXN_ADD)
+ return;

cpuhw->group_flag &= ~PERF_EVENT_TXN;
perf_pmu_enable(pmu);
@@ -1621,7 +1640,15 @@ static int power_pmu_commit_txn(struct pmu *pmu)

if (!ppmu)
return -EAGAIN;
+
cpuhw = this_cpu_ptr(&cpu_hw_events);
+ WARN_ON_ONCE(!cpuhw->txn_flags); /* no txn in flight */
+
+ if (cpuhw->txn_flags & ~PERF_PMU_TXN_ADD) {
+ cpuhw->txn_flags = 0;
+ return 0;
+ }
+
n = cpuhw->n_events;
if (check_excludes(cpuhw->event, cpuhw->flags, 0, n))
return -EAGAIN;
@@ -1633,6 +1660,7 @@ static int power_pmu_commit_txn(struct pmu *pmu)
cpuhw->event[i]->hw.config = cpuhw->events[i];

cpuhw->group_flag &= ~PERF_EVENT_TXN;
+ cpuhw->txn_flags = 0;
perf_pmu_enable(pmu);
return 0;
}
diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c
index 56fdad4..dbcfd29 100644
--- a/arch/s390/kernel/perf_cpum_cf.c
+++ b/arch/s390/kernel/perf_cpum_cf.c
@@ -72,6 +72,7 @@ struct cpu_hw_events {
atomic_t ctr_set[CPUMF_CTR_SET_MAX];
u64 state, tx_state;
unsigned int flags;
+ unsigned int txn_flags;
};
static DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = {
.ctr_set = {
@@ -82,6 +83,7 @@ static DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = {
},
.state = 0,
.flags = 0,
+ .txn_flags = 0,
};

static int get_counter_set(u64 event)
@@ -572,11 +574,21 @@ static void cpumf_pmu_del(struct perf_event *event, int flags)
/*
* Start group events scheduling transaction.
* Set flags to perform a single test at commit time.
+ *
+ * We only support PERF_PMU_TXN_ADD transactions. Save the
+ * transaction flags but otherwise ignore non-PERF_PMU_TXN_ADD
+ * transactions.
*/
-static void cpumf_pmu_start_txn(struct pmu *pmu)
+static void cpumf_pmu_start_txn(struct pmu *pmu, unsigned int txn_flags)
{
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);

+ WARN_ON_ONCE(cpuhw->txn_flags); /* txn already in flight */
+
+ cpuhw->txn_flags = txn_flags;
+ if (txn_flags & ~PERF_PMU_TXN_ADD)
+ return;
+
perf_pmu_disable(pmu);
cpuhw->flags |= PERF_EVENT_TXN;
cpuhw->tx_state = cpuhw->state;
@@ -589,8 +601,16 @@ static void cpumf_pmu_start_txn(struct pmu *pmu)
*/
static void cpumf_pmu_cancel_txn(struct pmu *pmu)
{
+ unsigned int txn_flags;
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);

+ WARN_ON_ONCE(!cpuhw->txn_flags); /* no txn in flight */
+
+ txn_flags = cphw->txn_flags;
+ cpuhw->txn_flags = 0;
+ if (txn_flags & ~PERF_PMU_TXN_ADD)
+ return;
+
WARN_ON(cpuhw->tx_state != cpuhw->state);

cpuhw->flags &= ~PERF_EVENT_TXN;
@@ -607,6 +627,13 @@ static int cpumf_pmu_commit_txn(struct pmu *pmu)
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
u64 state;

+ WARN_ON_ONCE(!cpuhw->txn_flags); /* no txn in flight */
+
+ if (cpuhw->txn_flags & ~PERF_PMU_TXN_ADD) {
+ cpuhw->txn_flags = 0;
+ return 0;
+ }
+
/* check if the updated state can be scheduled */
state = cpuhw->state & ~((1 << CPUMF_LCCTL_ENABLE_SHIFT) - 1);
state >>= CPUMF_LCCTL_ENABLE_SHIFT;
@@ -614,6 +641,7 @@ static int cpumf_pmu_commit_txn(struct pmu *pmu)
return -EPERM;

cpuhw->flags &= ~PERF_EVENT_TXN;
+ cpuhw->txn_flags = 0;
perf_pmu_enable(pmu);
return 0;
}
diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
index e3f89c7..2c0984d 100644
--- a/arch/sparc/kernel/perf_event.c
+++ b/arch/sparc/kernel/perf_event.c
@@ -109,6 +109,7 @@ struct cpu_hw_events {
int enabled;

unsigned int group_flag;
+ unsigned int txn_flags;
};
static DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = { .enabled = 1, };

@@ -1494,10 +1495,16 @@ static int sparc_pmu_event_init(struct perf_event *event)
* Set the flag to make pmu::enable() not perform the
* schedulability test, it will be performed at commit time
*/
-static void sparc_pmu_start_txn(struct pmu *pmu)
+static void sparc_pmu_start_txn(struct pmu *pmu, unsigned int txn_flags)
{
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);

+ WARN_ON_ONCE(cpuhw->txn_flags); /* txn already in flight */
+
+ cpuhw->txn_flags = txn_flags;
+ if (txn_flags & ~PERF_PMU_TXN_ADD)
+ return;
+
perf_pmu_disable(pmu);
cpuhw->group_flag |= PERF_EVENT_TXN;
}
@@ -1510,6 +1517,14 @@ static void sparc_pmu_start_txn(struct pmu *pmu)
static void sparc_pmu_cancel_txn(struct pmu *pmu)
{
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
+ unsigned int txn_flags;
+
+ WARN_ON_ONCE(!cpuhw->txn_flags); /* no txn in flight */
+
+ txn_flags = cpuhw->txn_flags;
+ cpuhw->txn_flags = 0;
+ if (txn_flags & ~PERF_PMU_TXN_ADD)
+ return;

cpuhw->group_flag &= ~PERF_EVENT_TXN;
perf_pmu_enable(pmu);
@@ -1528,6 +1543,13 @@ static int sparc_pmu_commit_txn(struct pmu *pmu)
if (!sparc_pmu)
return -EINVAL;

+ WARN_ON_ONCE(!cpuc->txn_flags); /* no txn in flight */
+
+ if (cpuc->txn_flags & ~PERF_PMU_TXN_ADD) {
+ cpuc->txn_flags = 0;
+ return 0;
+ }
+
n = cpuc->n_events;
if (check_excludes(cpuc->event, 0, n))
return -EINVAL;
@@ -1535,6 +1557,7 @@ static int sparc_pmu_commit_txn(struct pmu *pmu)
return -EAGAIN;

cpuc->group_flag &= ~PERF_EVENT_TXN;
+ cpuc->txn_flags = 0;
perf_pmu_enable(pmu);
return 0;
}
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 66dd3fe9..dc77ef4 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1748,9 +1748,21 @@ static inline void x86_pmu_read(struct perf_event *event)
* Start group events scheduling transaction
* Set the flag to make pmu::enable() not perform the
* schedulability test, it will be performed at commit time
+ *
+ * We only support PERF_PMU_TXN_ADD transactions. Save the
+ * transaction flags but otherwise ignore non-PERF_PMU_TXN_ADD
+ * transactions.
*/
-static void x86_pmu_start_txn(struct pmu *pmu)
+static void x86_pmu_start_txn(struct pmu *pmu, unsigned int txn_flags)
{
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+ WARN_ON_ONCE(cpuc->txn_flags); /* txn already in flight */
+
+ cpuc->txn_flags = txn_flags;
+ if (txn_flags & ~PERF_PMU_TXN_ADD)
+ return;
+
perf_pmu_disable(pmu);
__this_cpu_or(cpu_hw_events.group_flag, PERF_EVENT_TXN);
__this_cpu_write(cpu_hw_events.n_txn, 0);
@@ -1763,6 +1775,16 @@ static void x86_pmu_start_txn(struct pmu *pmu)
*/
static void x86_pmu_cancel_txn(struct pmu *pmu)
{
+ unsigned int txn_flags;
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+ WARN_ON_ONCE(!cpuc->txn_flags); /* no txn in flight */
+
+ txn_flags = cpuc->txn_flags;
+ cpuc->txn_flags = 0;
+ if (txn_flags & ~PERF_PMU_TXN_ADD)
+ return;
+
__this_cpu_and(cpu_hw_events.group_flag, ~PERF_EVENT_TXN);
/*
* Truncate collected array by the number of events added in this
@@ -1786,6 +1808,13 @@ static int x86_pmu_commit_txn(struct pmu *pmu)
int assign[X86_PMC_IDX_MAX];
int n, ret;

+ WARN_ON_ONCE(!cpuc->txn_flags); /* no txn in flight */
+
+ if (cpuc->txn_flags & ~PERF_PMU_TXN_ADD) {
+ cpuc->txn_flags = 0;
+ return 0;
+ }
+
n = cpuc->n_events;

if (!x86_pmu_initialized())
@@ -1802,6 +1831,7 @@ static int x86_pmu_commit_txn(struct pmu *pmu)
memcpy(cpuc->assign, assign, n*sizeof(int));

cpuc->group_flag &= ~PERF_EVENT_TXN;
+ cpuc->txn_flags = 0;
perf_pmu_enable(pmu);
return 0;
}
diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index 5edf6d8..c99c93b 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -196,6 +196,7 @@ struct cpu_hw_events {
int n_excl; /* the number of exclusive events */

unsigned int group_flag;
+ unsigned int txn_flags;
int is_fake;

/*
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 092a0e8..4e8d780 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -168,6 +168,8 @@ struct perf_event;
*/
#define PERF_EVENT_TXN 0x1

+#define PERF_PMU_TXN_ADD 0x1 /* txn to add/schedule event on PMU */
+
/**
* pmu::capabilities flags
*/
@@ -252,20 +254,26 @@ struct pmu {
*
* Start the transaction, after this ->add() doesn't need to
* do schedulability tests.
+ *
+ * Optional.
*/
- void (*start_txn) (struct pmu *pmu); /* optional */
+ void (*start_txn) (struct pmu *pmu, unsigned int txn_flags);
/*
* If ->start_txn() disabled the ->add() schedulability test
* then ->commit_txn() is required to perform one. On success
* the transaction is closed. On error the transaction is kept
* open until ->cancel_txn() is called.
+ *
+ * Optional.
*/
- int (*commit_txn) (struct pmu *pmu); /* optional */
+ int (*commit_txn) (struct pmu *pmu);
/*
* Will cancel the transaction, assumes ->del() is called
* for each successful ->add() during the transaction.
+ *
+ * Optional.
*/
- void (*cancel_txn) (struct pmu *pmu); /* optional */
+ void (*cancel_txn) (struct pmu *pmu);

/*
* Will return the value for perf_event_mmap_page::index for this event,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index e818389..e221432 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1914,7 +1914,7 @@ group_sched_in(struct perf_event *group_event,
if (group_event->state == PERF_EVENT_STATE_OFF)
return 0;

- pmu->start_txn(pmu);
+ pmu->start_txn(pmu, PERF_PMU_TXN_ADD);

if (event_sched_in(group_event, cpuctx, ctx)) {
pmu->cancel_txn(pmu);
@@ -7267,24 +7267,49 @@ static void perf_pmu_nop_void(struct pmu *pmu)
{
}

+static void perf_pmu_nop_txn(struct pmu *pmu, unsigned int flags)
+{
+}
+
static int perf_pmu_nop_int(struct pmu *pmu)
{
return 0;
}

-static void perf_pmu_start_txn(struct pmu *pmu)
+DEFINE_PER_CPU(unsigned int, nop_txn_flags);
+
+static void perf_pmu_start_txn(struct pmu *pmu, unsigned int flags)
{
+ __this_cpu_write(nop_txn_flags, flags);
+
+ if (flags & ~PERF_PMU_TXN_ADD)
+ return;
+
perf_pmu_disable(pmu);
}

static int perf_pmu_commit_txn(struct pmu *pmu)
{
+ unsigned int flags = __this_cpu_read(nop_txn_flags);
+
+ __this_cpu_write(nop_txn_flags, 0);
+
+ if (flags & ~PERF_PMU_TXN_ADD)
+ return 0;
+
perf_pmu_enable(pmu);
return 0;
}

static void perf_pmu_cancel_txn(struct pmu *pmu)
{
+ unsigned int flags = __this_cpu_read(nop_txn_flags);
+
+ __this_cpu_write(nop_txn_flags, 0);
+
+ if (flags & ~PERF_PMU_TXN_ADD)
+ return;
+
perf_pmu_enable(pmu);
}

@@ -7523,7 +7548,7 @@ got_cpu_context:
pmu->commit_txn = perf_pmu_commit_txn;
pmu->cancel_txn = perf_pmu_cancel_txn;
} else {
- pmu->start_txn = perf_pmu_nop_void;
+ pmu->start_txn = perf_pmu_nop_txn;
pmu->commit_txn = perf_pmu_nop_int;
pmu->cancel_txn = perf_pmu_nop_void;
}
--
1.7.9.5


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