Messages in this thread | | | Date | Tue, 27 Sep 2022 13:36:53 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 12/23] thermal: intel: hfi: Convert table_lock to use flags-handling variants |
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On Tue, Sep 27, 2022 at 01:34:07PM +0200, Peter Zijlstra wrote: > 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.
Anyway; given the existence of this here loop; why not have something like:
DEFINE_PER_CPU(int, hfi_ipc_class);
class = // extract from HFI mess WRITE_ONCE(per_cpu(hfi_ipc_class, cpu), class);
And then have the tick use this_cpu_read(hfi_ipc_class)? No extra locking required.
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