[RFC] arch: custom _current implementation - alt
#81153
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rruuaanng
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Add the following arch-specific APIs: - arch_curr_thread() - arch_set_curr_thread() which allow SMP architectures to implement a faster "get current thread pointer" than the default provided by the kernel. The 'set' function is required for the 'get' to work, more on that later. When `CONFIG_ARCH_HAS_CUSTOM_CURRENT_IMPL` is selected, calls to `_current` & `k_sched_current_thread_query()` will be redirected to `arch_curr_thread()`, which ideally should translate into a single instruction read, avoiding the current "lock > read CPU > read current thread > unlock" path in SMP architectures and thus greatly improves the read performance. However, since the kernel relies on a copy of the "current thread"s on every CPU for certain operations (i.e. to compare the priority of the currently scheduled thread on another CPU to determine if IPI should be sent), we can't eliminate the copy of "current thread" (`current`) from the `struct _cpu` and therefore the kernel now has to invoke `arch_set_curr_thread()` in addition to what it has been doing. This means that it will take slightly longer (most likely one instruction write) to change the current thread pointer on the current CPU. Signed-off-by: Yong Cong Sin <[email protected]> Signed-off-by: Yong Cong Sin <[email protected]>
Implement `arch_curr_thread()` & `arch_set_curr_thread()` with the global pointer (GP) register. Signed-off-by: Yong Cong Sin <[email protected]> Signed-off-by: Yong Cong Sin <[email protected]>
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See #80716