Quoting Tvrtko Ursulin (2020-10-20 17:11:44)
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> Since we keep a driver global mask of online CPUs and base the decision
> whether PMU needs to be migrated upon it, we need to make sure the
> migration is done for all registered PMUs (so GPUs).
>
> To do this we need to track the current CPU for each PMU and base the
> decision on whether to migrate on a comparison between global and local
> state.
>
> At the same time, since dynamic CPU hotplug notification slots are a
> scarce resource and given how we already register the multi instance type
> state, we can and should add multiple instance of the i915 PMU to this
> same state and not allocate a new one for every GPU.
>
> v2:
> * Use pr_notice. (Chris)
>
> v3:
> * Handle a nasty interaction where unregistration which triggers a false
> CPU offline event. (Chris)
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Suggested-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> # dynamic slot optimisation
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_pci.c | 7 +++-
> drivers/gpu/drm/i915/i915_pmu.c | 57 +++++++++++++++++++++------------
> drivers/gpu/drm/i915/i915_pmu.h | 6 +++-
> 3 files changed, 48 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
> index 27964ac0638a..a384f51c91c1 100644
> --- a/drivers/gpu/drm/i915/i915_pci.c
> +++ b/drivers/gpu/drm/i915/i915_pci.c
> @@ -1150,9 +1150,13 @@ static int __init i915_init(void)
> return 0;
> }
>
> + i915_pmu_init();
> +
> err = pci_register_driver(&i915_pci_driver);
> - if (err)
> + if (err) {
> + i915_pmu_exit();
> return err;
We could do an onion bhaji and call i915_globals_exit() as well.
> + }
>
> i915_perf_sysctl_register();
> return 0;
> @@ -1166,6 +1170,7 @@ static void __exit i915_exit(void)
> i915_perf_sysctl_unregister();
> pci_unregister_driver(&i915_pci_driver);
> i915_globals_exit();
> + i915_pmu_exit();
pmu_exit then globals_exit to pair with i915_init?
> }
>
> module_init(i915_init);
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index 51ed7d0efcdc..cd786ad12be7 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.c
> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> @@ -30,6 +30,7 @@
> #define ENGINE_SAMPLE_BITS (1 << I915_PMU_SAMPLE_BITS)
>
> static cpumask_t i915_pmu_cpumask;
> +static unsigned int i915_pmu_target_cpu = -1;
>
> static u8 engine_config_sample(u64 config)
> {
> @@ -1049,25 +1050,39 @@ static int i915_pmu_cpu_online(unsigned int cpu, struct hlist_node *node)
> static int i915_pmu_cpu_offline(unsigned int cpu, struct hlist_node *node)
> {
> struct i915_pmu *pmu = hlist_entry_safe(node, typeof(*pmu), cpuhp.node);
> - unsigned int target;
> + unsigned int target = i915_pmu_target_cpu;
>
> GEM_BUG_ON(!pmu->base.event_init);
>
> + /*
> + * Unregistering an instance generates a CPU offline event which we must
> + * ignore to avoid incorrectly modifying the shared i915_pmu_cpumask.
> + */
> + if (pmu->closed)
> + return 0;
> +
> if (cpumask_test_and_clear_cpu(cpu, &i915_pmu_cpumask)) {
> target = cpumask_any_but(topology_sibling_cpumask(cpu), cpu);
> +
> /* Migrate events if there is a valid target */
> if (target < nr_cpu_ids) {
> cpumask_set_cpu(target, &i915_pmu_cpumask);
> - perf_pmu_migrate_context(&pmu->base, cpu, target);
> + i915_pmu_target_cpu = target;
> }
> }
>
> + if (target < nr_cpu_ids && target != pmu->cpuhp.cpu) {
> + perf_pmu_migrate_context(&pmu->base, cpu, target);
> + pmu->cpuhp.cpu = target;
> + }
> +
> return 0;
> }
>
> -static int i915_pmu_register_cpuhp_state(struct i915_pmu *pmu)
> +static enum cpuhp_state cpuhp_slot = CPUHP_INVALID;
> +
> +void i915_pmu_init(void)
> {
> - enum cpuhp_state slot;
> int ret;
>
> ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN,
> @@ -1075,27 +1090,29 @@ static int i915_pmu_register_cpuhp_state(struct i915_pmu *pmu)
> i915_pmu_cpu_online,
> i915_pmu_cpu_offline);
> if (ret < 0)
> - return ret;
> + pr_notice("Failed to setup cpuhp state for i915 PMU! (%d)\n",
> + ret);
> + else
> + cpuhp_slot = ret;
> +}
>
> - slot = ret;
> - ret = cpuhp_state_add_instance(slot, &pmu->cpuhp.node);
> - if (ret) {
> - cpuhp_remove_multi_state(slot);
> - return ret;
> - }
> +void i915_pmu_exit(void)
> +{
> + if (cpuhp_slot != CPUHP_INVALID)
> + cpuhp_remove_multi_state(cpuhp_slot);
> +}
>
> - pmu->cpuhp.slot = slot;
> - return 0;
> +static int i915_pmu_register_cpuhp_state(struct i915_pmu *pmu)
> +{
> + if (cpuhp_slot == CPUHP_INVALID)
> + return -EINVAL;
> +
> + return cpuhp_state_add_instance(cpuhp_slot, &pmu->cpuhp.node);
> }
>
> static void i915_pmu_unregister_cpuhp_state(struct i915_pmu *pmu)
> {
> - struct drm_i915_private *i915 = container_of(pmu, typeof(*i915), pmu);
> -
> - drm_WARN_ON(&i915->drm, pmu->cpuhp.slot == CPUHP_INVALID);
> - drm_WARN_ON(&i915->drm, cpuhp_state_remove_instance(pmu->cpuhp.slot, &pmu->cpuhp.node));
> - cpuhp_remove_multi_state(pmu->cpuhp.slot);
> - pmu->cpuhp.slot = CPUHP_INVALID;
> + cpuhp_state_remove_instance(cpuhp_slot, &pmu->cpuhp.node);
> }
>
> static bool is_igp(struct drm_i915_private *i915)
> @@ -1129,7 +1146,7 @@ void i915_pmu_register(struct drm_i915_private *i915)
> spin_lock_init(&pmu->lock);
> hrtimer_init(&pmu->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> pmu->timer.function = i915_sample;
> - pmu->cpuhp.slot = CPUHP_INVALID;
> + pmu->cpuhp.cpu = -1;
To the best of my limited understanding of cpuhp,
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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