Re: [PATCH v1] riscv: irqflags: Conditionally enable interrupts in arch_local_irq_restore()

[Jisheng Zhang <jszhang@kernel.org>]

On Tue, Nov 10, 2026 at 04:50:38PM -0600, Andy Chiu wrote:
> From: Anton Blanchard <antonb@tenstorrent.com>
> 
> The Tenstorrent Ascalon core has an optimization that reduces pipeline
> synchronisation for immediate writes of SIE. This optimization does not
> work with register-based CSR writes, which occur when restoring flags in
> arch_local_irq_restore().
> 
> Refactor arch_local_irq_restore() to conditionally call
> arch_local_irq_enable() only when saved flags indicate interrupts were
> enabled.
> 
> On a simple nginx benchmark serving a small static HTML file this patch
> improves performance by 4%.
> 
> Signed-off-by: Anton Blanchard <antonb@tenstorrent.com>
> Co-developed-by: Nicholas Piggin <npiggin@oss.tenstorrent.com>
> Signed-off-by: Nicholas Piggin <npiggin@oss.tenstorrent.com>
> Signed-off-by: Andy Chiu <tchiu@tenstorrent.com>

Reviewed-by: Jisheng Zhang <jszhang@kernel.org>

> ---
>  arch/riscv/include/asm/irqflags.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/irqflags.h b/arch/riscv/include/asm/irqflags.h
> index 6fd8cbfcfcc7..5b1bca17bdc4 100644
> --- a/arch/riscv/include/asm/irqflags.h
> +++ b/arch/riscv/include/asm/irqflags.h
> @@ -48,7 +48,8 @@ static inline int arch_irqs_disabled(void)
>  /* set interrupt enabled status */
>  static inline void arch_local_irq_restore(unsigned long flags)
>  {
> -	csr_set(CSR_STATUS, flags & SR_IE);
> +	if (!arch_irqs_disabled_flags(flags))
> +		arch_local_irq_enable();
>  }
>  
>  #endif /* _ASM_RISCV_IRQFLAGS_H */
> 
> base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
> -- 
> 2.43.0
> 
> 
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