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

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Date: Wed, 10 Jan 2024 07:47:48 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Yangyu Chen <cyy@...self.name>, linux-riscv@...ts.infradead.org
Cc: 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>, Jisheng Zhang
 <jszhang@...nel.org>, Andrew Waterman <andrew@...ive.com>
Subject: Re: [PATCH] RISC-V: only flush icache when it has VM_EXEC set

Hi Yangyu,

On 09/01/2024 19:48, 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


Which platform did you test this patchset? Do you have any measurement 
of the performance improvements?


> copy_from_user_page is needed such as profiling with perf.
>
> 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)


Otherwise, it looks good to me, so you can add:

Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks,

Alex