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Date: Thu, 11 Apr 2024 00:27:00 +0530
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Subject: Re: [PATCH v4 3/4] arm64: Update AMU-based frequency scale factor on
 entering idle
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To: Beata Michalska <beata.michalska@arm.com>, <linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>, <ionela.voinescu@arm.com>,
	<vanshikonda@os.amperecomputing.com>
CC: <sudeep.holla@arm.com>, <will@kernel.org>, <catalin.marinas@arm.com>,
	<vincent.guittot@linaro.org>, <yang@os.amperecomputing.com>,
	<lihuisong@huawei.com>, linux-tegra <linux-tegra@vger.kernel.org>
References: <20240405133319.859813-1-beata.michalska@arm.com>
 <20240405133319.859813-4-beata.michalska@arm.com>
From: Sumit Gupta <sumitg@nvidia.com>
In-Reply-To: <20240405133319.859813-4-beata.michalska@arm.com>
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Hi Beata,

This patch is giving abort due to 'amu_fie_cpus' mask which gets 
allocated later in 'init_amu_fie()'.

  ] smp: Bringing up secondary CPUs ...
  ] Unable to handle kernel read from unreadable memory at virtual
    address 0000000000000000
    .......
  ] Call trace:
  ]  arch_cpu_idle_enter+0x30/0xe0
  ]  do_idle+0xb8/0x2e0
  ]  cpu_startup_entry+0x3c/0x50
  ]  rest_init+0x108/0x128
  ]  start_kernel+0x7a4/0xa50
  ]  __primary_switched+0x80/0x90
  ] Code: d53cd042 b8626800 f943c821 53067c02 (f8627821)
  ] ---[ end trace 0000000000000000 ]---
  ] Kernel panic - not syncing: Oops: Fatal exception

Added cpumask_available() check before access to fix.

  +++ b/arch/arm64/kernel/topology.c
  @@ -211,9 +211,13 @@ void arch_cpu_idle_enter(void)
   {
          unsigned int cpu = smp_processor_id();

  -       if (!cpumask_test_cpu(cpu, amu_fie_cpus))
  +       if (cpumask_available(amu_fie_cpus) &&
  +           !cpumask_test_cpu(cpu, amu_fie_cpus))
                  return;

Thank you,
Sumit Gupta

On 05/04/24 19:03, Beata Michalska wrote:
> External email: Use caution opening links or attachments
> 
> 
> Now that the frequency scale factor has been activated for retrieving
> current frequency on a given CPU, trigger its update upon entering
> idle. This will, to an extent, allow querying last known frequency
> in a non-invasive way. It will also improve the frequency scale factor
> accuracy when a CPU entering idle did not receive a tick for a while.
> As a consequence, for idle cores, the reported frequency will be the
> last one observed before entering the idle state.
> 
> Suggested-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
> Signed-off-by: Beata Michalska <beata.michalska@arm.com>
> ---
>   arch/arm64/kernel/topology.c | 17 +++++++++++++++--
>   1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index b03fe8617721..f204f6489f98 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -207,6 +207,19 @@ static struct scale_freq_data amu_sfd = {
>          .set_freq_scale = amu_scale_freq_tick,
>   };
> 
> +void arch_cpu_idle_enter(void)
> +{
> +       unsigned int cpu = smp_processor_id();
> +
> +       if (!cpumask_test_cpu(cpu, amu_fie_cpus))
> +               return;
> +
> +       /* Kick in AMU update but only if one has not happened already */
> +       if (housekeeping_cpu(cpu, HK_TYPE_TICK) &&
> +           time_is_before_jiffies(per_cpu(cpu_amu_samples.last_update, cpu)))
> +               amu_scale_freq_tick();
> +}
> +
>   #define AMU_SAMPLE_EXP_MS      20
> 
>   unsigned int arch_freq_get_on_cpu(int cpu)
> @@ -232,8 +245,8 @@ unsigned int arch_freq_get_on_cpu(int cpu)
>           * this boils down to identifying an active cpu within the same freq
>           * domain, if any.
>           */
> -       if (!housekeeping_cpu(cpu, HK_TYPE_TICK) ||
> -           time_is_before_jiffies(last_update + msecs_to_jiffies(AMU_SAMPLE_EXP_MS))) {
> +       if (!housekeeping_cpu(cpu, HK_TYPE_TICK) || (!idle_cpu(cpu) &&
> +           time_is_before_jiffies(last_update + msecs_to_jiffies(AMU_SAMPLE_EXP_MS)))) {
>                  struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
>                  int ref_cpu = cpu;
> 
> --
> 2.25.1
>