[PATCH v5 7/8] Define PERF_PMU_TXN_READ interface
From: Sukadev Bhattiprolu <hidden>
Date: 2015-08-14 06:52:07
Also in:
linux-s390, lkml, sparclinux
Subsystem:
performance events subsystem, the rest · Maintainers:
Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Linus Torvalds
Define a new PERF_PMU_TXN_READ interface to read a group of counters
at once.
pmu->start_txn() // Initialize before first event
for each event in group
pmu->read(event); // Queue each event to be read
rc = pmu->commit_txn() // Read/update all queued counters
Note that we use this interface with all PMUs. PMUs that implement this
interface use the ->read() operation to _queue_ the counters to be read
and use ->commit_txn() to actually read all the queued counters at once.
PMUs that don't implement PERF_PMU_TXN_READ ignore ->start_txn() and
->commit_txn() and continue to read counters one at a time.
Thanks to input from Peter Zijlstra.
Signed-off-by: Sukadev Bhattiprolu <redacted>
---
Changelog[v4]
- [Peter Zijlstra] Add lockdep_assert_held() in perf_event_read_group().
Make sure the entire transaction happens on the same CPU.
---
include/linux/perf_event.h | 1 +
kernel/events/core.c | 24 +++++++++++++++++++-----
2 files changed, 20 insertions(+), 5 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 44bf05f..da307ad 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h@@ -169,6 +169,7 @@ struct perf_event; #define PERF_EVENT_TXN 0x1 #define PERF_PMU_TXN_ADD 0x1 /* txn to add/schedule event on PMU */ +#define PERF_PMU_TXN_READ 0x2 /* txn to read event group from PMU */ /** * pmu::capabilities flags
diff --git a/kernel/events/core.c b/kernel/events/core.c
index e3ce047..fde2f43 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c@@ -3189,6 +3189,7 @@ static void __perf_event_read(void *info) struct perf_event *sub, *event = data->event; struct perf_event_context *ctx = event->ctx; struct perf_cpu_context *cpuctx = __get_cpu_context(ctx); + struct pmu *pmu = event->pmu; /* * If this is a task context, we need to check whether it is
@@ -3207,18 +3208,31 @@ static void __perf_event_read(void *info) } update_event_times(event); - if (event->state == PERF_EVENT_STATE_ACTIVE) - event->pmu->read(event); + if (event->state != PERF_EVENT_STATE_ACTIVE) + goto unlock; - if (!data->group) + if (!data->group) { + pmu->read(event); + data->ret = 0; goto unlock; + } + + pmu->start_txn(pmu, PERF_PMU_TXN_READ); + + pmu->read(event); list_for_each_entry(sub, &event->sibling_list, group_entry) { update_event_times(sub); - if (sub->state == PERF_EVENT_STATE_ACTIVE) + if (sub->state == PERF_EVENT_STATE_ACTIVE) { + /* + * Use sibling's PMU rather than @event's since + * sibling could be on different (eg: software) PMU. + */ sub->pmu->read(sub); + } } - data->ret = 0; + + data->ret = pmu->commit_txn(pmu); unlock: raw_spin_unlock(&ctx->lock);
--
1.7.9.5