Fix two deficiencies in the CPU frequency scaling subsystem #98459
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ZhaoxiangJin
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peter-mitsis
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seankyer
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@kartben Should this be added to 4.3 release? Is there a label that must be added? |
ZhaoxiangJin
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subsys/cpu_freq/cpu_freq.c
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| target_cpus = (num_cpus == 32U) ? 0xFFFFFFFF : (1U << num_cpus) - 1U; | ||
| target_cpus ^= (1U << _current_cpu->id), |
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Nit: typo?
Suggested change
| target_cpus ^= (1U << _current_cpu->id), | |
| target_cpus ^= (1U << _current_cpu->id); |
| uint32_t target_cpus; | ||
| int ret; | ||
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| __ASSERT(num_cpus <= 32U, "Too many CPUs"); |
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Outside PR scope: maybe the Kconfig for CPUFreq should impose range 1 32 to CONFIG_MP_MAX_NUM_CPUS instead?
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It might be more appropriate to create a separate PR for a global update.
doc/services/cpu_freq/index.rst
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| The SoC supporting CPU Frequency Scaling must uphold Zephyr's requirement that the system timer remains | ||
| constant over the lifetime of the program. See :ref:`Kernel Timing <kernel_timing>` for more information. |
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Quoting the part of the Kernel Timing page which I think this is referring (emphasis mine):
The frequency of [the system timer] counter is required to be steady over time
Proposal:
Suggested change
| The SoC supporting CPU Frequency Scaling must uphold Zephyr's requirement that the system timer remains | |
| constant over the lifetime of the program. See :ref:`Kernel Timing <kernel_timing>` for more information. | |
| The SoC supporting CPU Frequency Scaling must uphold Zephyr's requirement that the system timer frequency | |
| remains steady over the lifetime of the program. See :ref:`Kernel Timing <kernel_timing>` for more information. |
In the current code, 'target_cpus ^= (1U << _current_cpu->id)' is first used to remove the current core. Then, k_ipi_work_add performs 'target_cpus ^ (1U << _current_cpu->id)' again when passing parameters. This will add the current core to the mask again, causing the current core to receive IPI and directly call cpu_freq_next_pstate() at the end, which may lead to duplicate execution. This commit changed 'target_cpus ^ (1U << _current_cpu->id)' to 'target_cpus' in k_ipi_work_add to avoid the second XOR. Signed-off-by: Zhaoxiang Jin <Zhaoxiang.Jin_1@nxp.com>
The current code calls cpu_freq_policy_reset() once within the SMP branch of the cpu_freq_timer_handler function, and then calls it again at the beginning of cpu_freq_next_pstate(). This causes repeated resets of 'pstate_best' and 'num_unprocessed_cpus', which prevents the 'last core' from being reached. The initiating core should perform a reset before broadcasting, and other cores should not reset again. Signed-off-by: Zhaoxiang Jin <Zhaoxiang.Jin_1@nxp.com>
Improve cpu_freq documentation. Signed-off-by: Zhaoxiang Jin <Zhaoxiang.Jin_1@nxp.com>
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Three changes in this PR:
k_ipi_work_addIn the current code,
target_cpus ^= (1U << _current_cpu->id)is first used to remove the current core. Then,k_ipi_work_addperformstarget_cpus ^ (1U << _current_cpu->id)again when passing parameters. This will add the current core to the mask again, causing the current core to receive IPI and directly callcpu_freq_next_pstate()at the end, which may lead to duplicate execution. This first change is to changetarget_cpus ^ (1U << _current_cpu->id)totarget_cpusink_ipi_work_addto avoid the second XOR.cpu_freq_policy_reset()The current code calls
cpu_freq_policy_reset()once within the SMP branch of thecpu_freq_timer_handlerfunction, and then calls it again at the beginning ofcpu_freq_next_pstate(). This causes repeated resets ofpstate_bestandnum_unprocessed_cpus, which prevents the 'last core' from being reached. The initiating core should perform a reset before broadcasting, and other cores should not reset again.cpu_freqdocumentation.