Re: [PATCH v4 3/4] arm64: Update AMU-based frequency scale factor on entering idle

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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@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Beata Michalska <beata.michalska@xxxxxxx>
---
  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





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