perf/x86/intel: Use context switch callback to flush LBR stack

Previous commit introduces context switch callback, its function
overlaps with the flush branch stack callback. So we can use the
context switch callback to flush LBR stack.

This patch adds code that uses the flush branch callback to
flush the LBR stack when task is being scheduled in. The callback
is enabled only when there are events use the LBR hardware. This
patch also removes all old flush branch stack code.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: eranian@google.com
Cc: jolsa@redhat.com
Link: http://lkml.kernel.org/r/1415156173-10035-4-git-send-email-kan.liang@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 77 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6c8b31b7efb6..f563ce767f93 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -153,7 +153,6 @@ enum event_type_t {
  */
 struct static_key_deferred perf_sched_events __read_mostly;
 static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
-static DEFINE_PER_CPU(atomic_t, perf_branch_stack_events);
 static DEFINE_PER_CPU(int, perf_sched_cb_usages);
 
 static atomic_t nr_mmap_events __read_mostly;
@@ -1240,9 +1239,6 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx)
         if (is_cgroup_event(event))
                 ctx->nr_cgroups++;
 
-        if (has_branch_stack(event))
-                ctx->nr_branch_stack++;
-
         list_add_rcu(&event->event_entry, &ctx->event_list);
         ctx->nr_events++;
         if (event->attr.inherit_stat)
@@ -1409,9 +1405,6 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
                         cpuctx->cgrp = NULL;
         }
 
-        if (has_branch_stack(event))
-                ctx->nr_branch_stack--;
-
         ctx->nr_events--;
         if (event->attr.inherit_stat)
                 ctx->nr_stat--;
@@ -2809,64 +2802,6 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
 }
 
 /*
- * When sampling the branck stack in system-wide, it may be necessary
- * to flush the stack on context switch. This happens when the branch
- * stack does not tag its entries with the pid of the current task.
- * Otherwise it becomes impossible to associate a branch entry with a
- * task. This ambiguity is more likely to appear when the branch stack
- * supports priv level filtering and the user sets it to monitor only
- * at the user level (which could be a useful measurement in system-wide
- * mode). In that case, the risk is high of having a branch stack with
- * branch from multiple tasks. Flushing may mean dropping the existing
- * entries or stashing them somewhere in the PMU specific code layer.
- *
- * This function provides the context switch callback to the lower code
- * layer. It is invoked ONLY when there is at least one system-wide context
- * with at least one active event using taken branch sampling.
- */
-static void perf_branch_stack_sched_in(struct task_struct *prev,
-                                       struct task_struct *task)
-{
-        struct perf_cpu_context *cpuctx;
-        struct pmu *pmu;
-        unsigned long flags;
-
-        /* no need to flush branch stack if not changing task */
-        if (prev == task)
-                return;
-
-        local_irq_save(flags);
-
-        rcu_read_lock();
-
-        list_for_each_entry_rcu(pmu, &pmus, entry) {
-                cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
-
-                /*
-                 * check if the context has at least one
-                 * event using PERF_SAMPLE_BRANCH_STACK
-                 */
-                if (cpuctx->ctx.nr_branch_stack > 0
-                    && pmu->flush_branch_stack) {
-
-                        perf_ctx_lock(cpuctx, cpuctx->task_ctx);
-
-                        perf_pmu_disable(pmu);
-
-                        pmu->flush_branch_stack();
-
-                        perf_pmu_enable(pmu);
-
-                        perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
-                }
-        }
-
-        rcu_read_unlock();
-
-        local_irq_restore(flags);
-}
-
-/*
  * Called from scheduler to add the events of the current task
  * with interrupts disabled.
  *
@@ -2898,10 +2833,6 @@ void __perf_event_task_sched_in(struct task_struct *prev,
         if (atomic_read(this_cpu_ptr(&perf_cgroup_events)))
                 perf_cgroup_sched_in(prev, task);
 
-        /* check for system-wide branch_stack events */
-        if (atomic_read(this_cpu_ptr(&perf_branch_stack_events)))
-                perf_branch_stack_sched_in(prev, task);
-
         if (__this_cpu_read(perf_sched_cb_usages))
                 perf_pmu_sched_task(prev, task, true);
 }
@@ -3480,10 +3411,6 @@ static void unaccount_event_cpu(struct perf_event *event, int cpu)
         if (event->parent)
                 return;
 
-        if (has_branch_stack(event)) {
-                if (!(event->attach_state & PERF_ATTACH_TASK))
-                        atomic_dec(&per_cpu(perf_branch_stack_events, cpu));
-        }
         if (is_cgroup_event(event))
                 atomic_dec(&per_cpu(perf_cgroup_events, cpu));
 }
@@ -7139,10 +7066,6 @@ static void account_event_cpu(struct perf_event *event, int cpu)
         if (event->parent)
                 return;
 
-        if (has_branch_stack(event)) {
-                if (!(event->attach_state & PERF_ATTACH_TASK))
-                        atomic_inc(&per_cpu(perf_branch_stack_events, cpu));
-        }
         if (is_cgroup_event(event))
                 atomic_inc(&per_cpu(perf_cgroup_events, cpu));
 }