Quoting Tvrtko Ursulin (2020-10-20 11:08:22)
> 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)
>
> 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 | 50 ++++++++++++++++++++-------------
> drivers/gpu/drm/i915/i915_pmu.h | 6 +++-
> 3 files changed, 41 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;
> + }
>
> 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();
> }
>
> module_init(i915_init);
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index 51ed7d0efcdc..0d6c0945621e 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 +1050,32 @@ 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;
So we still have multiple callbacks, one per pmu. But each callback is
now stored in a list from the cpuhp_slot instead of each callback having
its own slot.
>
> GEM_BUG_ON(!pmu->base.event_init);
>
> if (cpumask_test_and_clear_cpu(cpu, &i915_pmu_cpumask)) {
On first callback...
> target = cpumask_any_but(topology_sibling_cpumask(cpu), cpu);
Pick any other 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;
Store target for all callbacks.
> }
> }
>
> + if (target < nr_cpu_ids && target != pmu->cpuhp.cpu) {
If global [i915_pmu_target_cpu] target has changed, update perf.
> + perf_pmu_migrate_context(&pmu->base, cpu, target);
> + pmu->cpuhp.cpu = target;
It is claimed that cpuhp_state_remove_instance() will call the offline
callback for all online cpus... Do we need a pmu->base.state != STOPPED
guard?
-Chris
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