linux-kernel - Re: [PATCH] RISC-V: only flush icache when it has VM

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Date: Mon, 15 Jan 2024 17:27:59 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Yangyu Chen <cyy@...self.name>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Conor Dooley <conor.dooley@...rochip.com>,
	Andrew Waterman <andrew@...ive.com>
Subject: Re: [PATCH] RISC-V: only flush icache when it has VM_EXEC set

On Wed, Jan 10, 2024 at 02:48:59AM +0800, Yangyu Chen wrote:
> As I-Cache flush on current RISC-V needs to send IPIs to every CPU cores
> in the system is very costly, limiting flush_icache_mm to be called only
> when vma->vm_flags has VM_EXEC can help minimize the frequency of these
> operations. It improves performance and reduces disturbances when
> copy_from_user_page is needed such as profiling with perf.

Hi Yangyu,

Since this is for "performance", can you please add the benchmark, test
platform and performance numbers in your commit msg?

thanks

> 
> For I-D coherence concerns, it will not fail if such a page adds VM_EXEC
> flags in the future since we have checked it in the __set_pte_at function.
> 
> Signed-off-by: Yangyu Chen <cyy@...self.name>
> ---
>  arch/riscv/include/asm/cacheflush.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
> index 3cb53c4df27c..915f532dc336 100644
> --- a/arch/riscv/include/asm/cacheflush.h
> +++ b/arch/riscv/include/asm/cacheflush.h
> @@ -33,8 +33,11 @@ static inline void flush_dcache_page(struct page *page)
>   * so instead we just flush the whole thing.
>   */
>  #define flush_icache_range(start, end) flush_icache_all()
> -#define flush_icache_user_page(vma, pg, addr, len) \
> -	flush_icache_mm(vma->vm_mm, 0)
> +#define flush_icache_user_page(vma, pg, addr, len)	\
> +do {							\
> +	if (vma->vm_flags & VM_EXEC)			\
> +		flush_icache_mm(vma->vm_mm, 0);		\
> +} while (0)
>  
>  #ifdef CONFIG_64BIT
>  #define flush_cache_vmap(start, end)	flush_tlb_kernel_range(start, end)
> -- 
> 2.43.0
>