riscv/context_switch: Set tp when a context switch occurs #15652
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This removes the need to call nxsched_self upon exception return. Later with a bit of added logic, it is possible to use tp in kernel to store and read the current tcb. Note: setting tp in riscv_restorecontext is too late for this, as this_task() points to the (next) ready-to-run task, thus tp should be updated when the rtr list is updated (via up_update_task, which does not exist for risc-v yet)
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Arch: risc-v
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Relates to this: #15563 |
lupyuen
approved these changes
Jan 22, 2025
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Tested OK on rv-virt:knsh. Thanks :-)
https://gist.github.com/lupyuen/e8760fd8fc6a59f7e524d17078f9bf23
nsh> uname -a
NuttX 10.4.0 0b8a64b715 Jan 22 2025 19:37:51 risc-v rv-virt
nsh> ostest
ostest_main: Exiting with status 0
xiaoxiang781216
approved these changes
Jan 22, 2025
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Summary
Restore kernel tp when an exception is taken, restore user tp when exception returns. Store kernel tp in CPU scratch
register when running user code.
This removes the need to call nxsched_self upon exception return. Later with a bit of added logic, it is possible to use tp in kernel to store and read the current tcb (read note).
Impact
Testing
rv-virt:knsh64 + ostest
Note: setting tp in riscv_restorecontext is too late for this, as this_task() points to the (next) ready-to-run task, thus tp should be updated when the rtr list is updated (via up_update_task, which does not exist for risc-v yet)