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Date: Wed, 22 Jul 2015 16:19:16 -0700
From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-s390@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v3 7/8] perf: Define PMU_TXN_READ interface
Peter Zijlstra [peterz@...radead.org] wrote:
| I've not woken up yet, and not actually fully read the email, but can
| you stuff the entire above chunk inside the IPI?
|
| I think you could then actually optimize __perf_event_read() as well,
| because all these events should be on the same context, so no point in
| calling update_*time*() for every event or so.
|
Do you mean something like this (will move the rename to a separate
patch before posting):
--
>From e8eddb5d3877ebdb3b71213a00aaa980f4010dd0 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Date: Tue, 7 Jul 2015 21:45:23 -0400
Subject: [PATCH 1/1] perf: Define PMU_TXN_READ interface
Define a new PERF_PMU_TXN_READ interface to read a group of counters
at once. 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 <sukadev@...ux.vnet.ibm.com>
---
Changelog[v5]
[Peter Zijlstra] Ensure the entire transaction happens on the same CPU.
Changelog[v4]
[Peter Zijlstra] Add lockdep_assert_held() in perf_event_read_group()
---
include/linux/perf_event.h | 1 +
kernel/events/core.c | 72 +++++++++++++++++++++++++++++++++++++-------
2 files changed, 62 insertions(+), 11 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 a6bd09d..7177dd8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3174,12 +3174,8 @@ void perf_event_exec(void)
rcu_read_unlock();
}
-/*
- * Cross CPU call to read the hardware event
- */
-static void __perf_event_read(void *info)
+static void __perf_event_read(struct perf_event *event, int update_ctx)
{
- struct perf_event *event = info;
struct perf_event_context *ctx = event->ctx;
struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
@@ -3194,7 +3190,7 @@ static void __perf_event_read(void *info)
return;
raw_spin_lock(&ctx->lock);
- if (ctx->is_active) {
+ if (ctx->is_active && update_ctx) {
update_context_time(ctx);
update_cgrp_time_from_event(event);
}
@@ -3204,6 +3200,16 @@ static void __perf_event_read(void *info)
raw_spin_unlock(&ctx->lock);
}
+/*
+ * Cross CPU call to read the hardware event
+ */
+static void __perf_event_read_ipi(void *info)
+{
+ struct perf_event *event = info;
+
+ __perf_event_read(event, 1);
+}
+
static inline u64 perf_event_count(struct perf_event *event)
{
if (event->pmu->count)
@@ -3220,7 +3226,7 @@ static void perf_event_read(struct perf_event *event)
*/
if (event->state == PERF_EVENT_STATE_ACTIVE) {
smp_call_function_single(event->oncpu,
- __perf_event_read, event, 1);
+ __perf_event_read_ipi, event, 1);
} else if (event->state == PERF_EVENT_STATE_INACTIVE) {
struct perf_event_context *ctx = event->ctx;
unsigned long flags;
@@ -3765,6 +3771,36 @@ static void orphans_remove_work(struct work_struct *work)
put_ctx(ctx);
}
+/*
+ * Use the transaction interface to read the group of events in @leader.
+ * PMUs like the 24x7 counters in Power, can use this to queue the events
+ * in the ->read() operation and perform the actual read in ->commit_txn.
+ *
+ * Other PMUs can ignore the ->start_txn and ->commit_txn and read each
+ * PMU directly in the ->read() operation.
+ */
+static int perf_event_read_group(struct perf_event *leader)
+{
+ int ret;
+ struct perf_event *sub;
+ struct pmu *pmu;
+ struct perf_event_context *ctx = leader->ctx;
+
+ lockdep_assert_held(&ctx->mutex);
+
+ pmu = leader->pmu;
+
+ pmu->start_txn(pmu, PERF_PMU_TXN_READ);
+
+ __perf_event_read(leader, 1);
+ list_for_each_entry(sub, &leader->sibling_list, group_entry)
+ __perf_event_read(sub, 0);
+
+ ret = pmu->commit_txn(pmu);
+
+ return ret;
+}
+
u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
{
u64 total = 0;
@@ -3794,7 +3830,17 @@ static int perf_read_group(struct perf_event *event,
lockdep_assert_held(&ctx->mutex);
- count = perf_event_read_value(leader, &enabled, &running);
+ mutex_lock(&leader->child_mutex);
+
+ ret = perf_event_read_group(leader);
+ if (ret) {
+ mutex_unlock(&leader->child_mutex);
+ return ret;
+ }
+
+ count = perf_event_aggregate(leader, &enabled, &running);
+
+ mutex_unlock(&leader->child_mutex);
values[n++] = 1 + leader->nr_siblings;
if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
@@ -3815,15 +3861,19 @@ static int perf_read_group(struct perf_event *event,
list_for_each_entry(sub, &leader->sibling_list, group_entry) {
n = 0;
- values[n++] = perf_event_read_value(sub, &enabled, &running);
+ mutex_lock(&sub->child_mutex);
+
+ values[n++] = perf_event_aggregate(sub, &enabled, &running);
+
+ mutex_unlock(&sub->child_mutex);
+
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(sub);
size = n * sizeof(u64);
- if (copy_to_user(buf + ret, values, size)) {
+ if (copy_to_user(buf + ret, values, size))
return -EFAULT;
- }
ret += size;
}
--
1.7.9.5
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