perf: Rewrite core context handling

There have been various issues and limitations with the way perf uses
(task) contexts to track events. Most notable is the single hardware
PMU task context, which has resulted in a number of yucky things (both
proposed and merged).

Notably:
 - HW breakpoint PMU
 - ARM big.little PMU / Intel ADL PMU
 - Intel Branch Monitoring PMU
 - AMD IBS PMU
 - S390 cpum_cf PMU
 - PowerPC trace_imc PMU

*Current design:*

Currently we have a per task and per cpu perf_event_contexts:

  task_struct::perf_events_ctxp[] <-> perf_event_context <-> perf_cpu_context
       ^                                 |    ^     |           ^
       `---------------------------------'    |     `--> pmu ---'
                                              v           ^
                                         perf_event ------'

Each task has an array of pointers to a perf_event_context. Each
perf_event_context has a direct relation to a PMU and a group of
events for that PMU. The task related perf_event_context's have a
pointer back to that task.

Each PMU has a per-cpu pointer to a per-cpu perf_cpu_context, which
includes a perf_event_context, which again has a direct relation to
that PMU, and a group of events for that PMU.

The perf_cpu_context also tracks which task context is currently
associated with that CPU and includes a few other things like the
hrtimer for rotation etc.

Each perf_event is then associated with its PMU and one
perf_event_context.

*Proposed design:*

New design proposed by this patch reduce to a single task context and
a single CPU context but adds some intermediate data-structures:

  task_struct::perf_event_ctxp -> perf_event_context <- perf_cpu_context
       ^                           |   ^ ^
       `---------------------------'   | |
                                       | |    perf_cpu_pmu_context <--.
                                       | `----.    ^                  |
                                       |      |    |                  |
                                       |      v    v                  |
                                       | ,--> perf_event_pmu_context  |
                                       | |                            |
                                       | |                            |
                                       v v                            |
                                  perf_event ---> pmu ----------------'

With the new design, perf_event_context will hold all events for all
pmus in the (respective pinned/flexible) rbtrees. This can be achieved
by adding pmu to rbtree key:

  {cpu, pmu, cgroup, group_index}

Each perf_event_context carries a list of perf_event_pmu_context which
is used to hold per-pmu-per-context state. For example, it keeps track
of currently active events for that pmu, a pmu specific task_ctx_data,
a flag to tell whether rotation is required or not etc.

Additionally, perf_cpu_pmu_context is used to hold per-pmu-per-cpu
state like hrtimer details to drive the event rotation, a pointer to
perf_event_pmu_context of currently running task and some other
ancillary information.

Each perf_event is associated to it's pmu, perf_event_context and
perf_event_pmu_context.

Further optimizations to current implementation are possible. For
example, ctx_resched() can be optimized to reschedule only single pmu
events.

Much thanks to Ravi for picking this up and pushing it towards
completion.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Co-developed-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20221008062424.313-1-ravi.bangoria@amd.com

1 files changed, 11 insertions, 7 deletions

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 7b0643fe2f13..54186542a969 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -806,10 +806,14 @@ static void armv8pmu_disable_event(struct perf_event *event)
 
 static void armv8pmu_start(struct arm_pmu *cpu_pmu)
 {
-	struct perf_event_context *task_ctx =
-		this_cpu_ptr(cpu_pmu->pmu.pmu_cpu_context)->task_ctx;
+	struct perf_event_context *ctx;
+	int nr_user = 0;
 
-	if (sysctl_perf_user_access && task_ctx && task_ctx->nr_user)
+	ctx = perf_cpu_task_ctx();
+	if (ctx)
+		nr_user = ctx->nr_user;
+
+	if (sysctl_perf_user_access && nr_user)
 		armv8pmu_enable_user_access(cpu_pmu);
 	else
 		armv8pmu_disable_user_access();
@@ -1019,10 +1023,10 @@ static int armv8pmu_set_event_filter(struct hw_perf_event *event,
 	return 0;
 }
 
-static int armv8pmu_filter_match(struct perf_event *event)
+static bool armv8pmu_filter(struct pmu *pmu, int cpu)
 {
-	unsigned long evtype = event->hw.config_base & ARMV8_PMU_EVTYPE_EVENT;
-	return evtype != ARMV8_PMUV3_PERFCTR_CHAIN;
+	struct arm_pmu *armpmu = to_arm_pmu(pmu);
+	return !cpumask_test_cpu(smp_processor_id(), &armpmu->supported_cpus);
 }
 
 static void armv8pmu_reset(void *info)
@@ -1253,7 +1257,7 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name,
 	cpu_pmu->stop			= armv8pmu_stop;
 	cpu_pmu->reset			= armv8pmu_reset;
 	cpu_pmu->set_event_filter	= armv8pmu_set_event_filter;
-	cpu_pmu->filter_match		= armv8pmu_filter_match;
+	cpu_pmu->filter			= armv8pmu_filter;
 
 	cpu_pmu->pmu.event_idx		= armv8pmu_user_event_idx;