linux-kernel - Re: [RFC PATCH 12/23] thermal: intel: hfi: Convert table

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Message-ID: <YzLfr49woc1PMOxO@hirez.programming.kicks-ass.net>
Date:   Tue, 27 Sep 2022 13:34:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [RFC PATCH 12/23] thermal: intel: hfi: Convert table_lock to use
 flags-handling variants

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.