Re: [RFC PATCH 12/23] thermal: intel: hfi: Convert table_lock to use flags-handling variants

Peter Zijlstra
2022-09-27T11:34:57Z

On Fri, Sep 09, 2022 at 04:11:54PM -0700, Ricardo Neri wrote:

> --- a/drivers/thermal/intel/intel_hfi.c
> +++ b/drivers/thermal/intel/intel_hfi.c
> @@ -175,9 +175,10 @@ static struct workqueue_struct *hfi_updates_wq;
> static void get_hfi_caps(struct hfi_instance *hfi_instance,
> struct thermal_genl_cpu_caps *cpu_caps)
> {
> + unsigned long flags;
> int cpu, i = 0;
>
> - raw_spin_lock_irq(&hfi_instance->table_lock);
> + raw_spin_lock_irqsave(&hfi_instance->table_lock, flags);
> for_each_cpu(cpu, hfi_instance->cpus) {
> struct hfi_cpu_data *caps;
> s16 index;

^^^^ Anti-pattern alert!

Now your IRQ latency depends on nr_cpus -- which is a fair fail. The
existing code is already pretty crap in that it has the preemption
latency depend on nr_cpus.

While I'm here looking at the HFI stuff, did they fix that HFI interrupt
broadcast mess already? Sending an interrupt to *all* CPUs is quite
insane.