linux-kernel - Re: [PATCH 4/4] riscv: enable HAVE_FAST

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Date: Sun, 31 Dec 2023 07:37:33 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Jisheng Zhang <jszhang@...nel.org>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Will Deacon <will@...nel.org>,
 "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Nick Piggin <npiggin@...il.com>,
 Peter Zijlstra <peterz@...radead.org>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-arch@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/4] riscv: enable HAVE_FAST_GUP if MMU

On 19/12/2023 18:50, Jisheng Zhang wrote:
> Activate the fast gup for riscv mmu platforms. Here are some
> GUP_FAST_BENCHMARK performance numbers:
>
> Before the patch:
> GUP_FAST_BENCHMARK: Time: get:53203 put:5085 us
>
> After the patch:
> GUP_FAST_BENCHMARK: Time: get:17711 put:5060 us


On which platform did you run this benchmark?


>
> The get time is reduced by 66.7%! IOW, 3x get speed!


Well done!

Thanks,

Alex


>
> Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> ---
>   arch/riscv/Kconfig               | 1 +
>   arch/riscv/include/asm/pgtable.h | 6 ++++++
>   2 files changed, 7 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index d3555173d9f4..04df9920282d 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -119,6 +119,7 @@ config RISCV
>   	select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER
>   	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
>   	select HAVE_EBPF_JIT if MMU
> +	select HAVE_FAST_GUP if MMU
>   	select HAVE_FUNCTION_ARG_ACCESS_API
>   	select HAVE_FUNCTION_ERROR_INJECTION
>   	select HAVE_GCC_PLUGINS
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index ab00235b018f..c6eb214139e6 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -673,6 +673,12 @@ static inline int pmd_write(pmd_t pmd)
>   	return pte_write(pmd_pte(pmd));
>   }
>   
> +#define pud_write pud_write
> +static inline int pud_write(pud_t pud)
> +{
> +	return pte_write(pud_pte(pud));
> +}
> +
>   static inline int pmd_dirty(pmd_t pmd)
>   {
>   	return pte_dirty(pmd_pte(pmd));