[PATCH 0/6] riscv: convert bottom half of exception handling to C

[Cyril Bur]

On Mon, Jun 17, 2024 at 3:21 AM Jisheng Zhang <jszhang at kernel.org> wrote:
>
> For readability, maintainability and future scalability, convert the
> bottom half of the exception handling to C.
>
> During the conversion, I found Anton fixed a performance issue
> and my patches will touch the same exception asm code, so I include
> Anton's patch for completeness. I also cooked a similar patch to avoid
> corrupting the RAS in ret_from_fork() per the inspiration.
>
> Mostly the assembly code is converted to C in a relatively
> straightforward manner.
>
> However, there are two modifications I need to mention:
>
> 1. the CSR_CAUSE reg reading and saving is moved to the C code
> because we need the cause to dispatch the exception handling,
> if we keep the cause reading and saving, we either pass it to
> do_traps() via. 2nd param or get it from pt_regs which an extra
> memory load is needed, I don't like any of the two solutions becase
> the exception handling sits in hot code path, every instruction
> matters.
>
> 2.To cope with SIFIVE_CIP_453 errata, it looks like we don't need
> alternative mechanism any more after the asm->c convertion. Just
> replace the excp_vect_table two entries.
>
>
>
> Anton Blanchard (1):
>   riscv: Improve exception and system call latency
>
I've retested this patch with the rest of the series applied. I can confirm
that the performance improvement is still there. Definitely thumbs up on my end.

> Jisheng Zhang (5):
>   riscv: avoid corrupting the RAS
>   riscv: convert bottom half of exception handling to C
>   riscv: errata: remove ALT_INSN_FAULT and ALT_PAGE_FAULT
>   riscv: errata: sifive: remove NOMMU handling
>   riscv: remove asmlinkage from updated functions
>
>  arch/riscv/errata/sifive/errata.c         | 25 +++++++---
>  arch/riscv/errata/sifive/errata_cip_453.S |  4 --
>  arch/riscv/include/asm/asm-prototypes.h   |  7 +--
>  arch/riscv/include/asm/errata_list.h      | 21 ++------
>  arch/riscv/kernel/entry.S                 | 61 ++---------------------
>  arch/riscv/kernel/stacktrace.c            |  4 +-
>  arch/riscv/kernel/traps.c                 | 57 ++++++++++++++++++---
>  7 files changed, 81 insertions(+), 98 deletions(-)
>
> --
> 2.43.0
>
>
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