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perf: Store active software events in a hashlist

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Each time a software event triggers, we need to walk through
the entire list of events from the current cpu and task contexts
to retrieve a running perf event that matches.
We also need to check a matching perf event is actually counting.

This walk is wasteful and makes the event fast path scaling
down with a growing number of events running on the same
contexts.

To solve this, we store the running perf events in a hashlist to
get an immediate access to them against their type:event_id when
they trigger.

v2: - Fix SWEVENT_HLIST_SIZE definition (and re-learn some basic
      maths along the way)
    - Only allocate hlist for online cpus, but keep track of the
      refcount on offline possible cpus too, so that we allocate it
      if needed when it becomes online.
    - Drop the kref use as it's not adapted to our tricks anymore.

v3: - Fix bad refcount check (address instead of value). Thanks to
      Eric Dumazet who spotted this.
    - While exiting cpu, move the hlist release out of the IPI path
      to lock the hlist mutex sanely.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Frederic Weisbecker
2010-04-05 15:35:57 +02:00
parent c055564217
commit 76e1d9047e
2 changed files with 196 additions and 64 deletions
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12
include/linux/perf_event.h
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@@ -589,6 +589,14 @@ enum perf_group_flag {
PERF_GROUP_SOFTWARE = 0x1,
};
#define SWEVENT_HLIST_BITS 8
#define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS)
struct swevent_hlist {
struct hlist_head heads[SWEVENT_HLIST_SIZE];
struct rcu_head rcu_head;
};
/**
* struct perf_event - performance event kernel representation:
*/
@@ -597,6 +605,7 @@ struct perf_event {
struct list_head group_entry;
struct list_head event_entry;
struct list_head sibling_list;
struct hlist_node hlist_entry;
int nr_siblings;
int group_flags;
struct perf_event *group_leader;
@@ -744,6 +753,9 @@ struct perf_cpu_context {
int active_oncpu;
int max_pertask;
int exclusive;
struct swevent_hlist *swevent_hlist;
struct mutex hlist_mutex;
int hlist_refcount;
/*
* Recursion avoidance: