linux-kernel - Re: [PATCH 3/3] riscv: pack rv64 thread

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Message-ID: <77437392-5d68-4620-ba05-08eba133b547@ghiti.fr>
Date: Fri, 25 Jul 2025 16:30:21 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Radim Krčmář <rkrcmar@...tanamicro.com>,
 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>,
 Deepak Gupta <debug@...osinc.com>
Subject: Re: [PATCH 3/3] riscv: pack rv64 thread_info better


On 7/22/25 18:05, Radim Krčmář wrote:
> On rv64, preempt_count and cpu were both 32-bit followed by 64-bit, so
> placing one in the hole saves 8 bytes in the struct.
>
> Signed-off-by: Radim Krčmář <rkrcmar@...tanamicro.com>
> ---
>   arch/riscv/include/asm/thread_info.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
> index f5916a70879a..c267d6bd838e 100644
> --- a/arch/riscv/include/asm/thread_info.h
> +++ b/arch/riscv/include/asm/thread_info.h
> @@ -53,6 +53,7 @@
>   struct thread_info {
>   	unsigned long		flags;		/* low level flags */
>   	int                     preempt_count;  /* 0=>preemptible, <0=>BUG */
> +	int			cpu;
>   	/*
>   	 * These stack pointers are overwritten on every system call or
>   	 * exception.  SP is also saved to the stack it can be recovered when
> @@ -60,7 +61,6 @@ struct thread_info {
>   	 */
>   	long			kernel_sp;	/* Kernel stack pointer */
>   	long			user_sp;	/* User stack pointer */
> -	int			cpu;
>   	unsigned long		syscall_work;	/* SYSCALL_WORK_ flags */
>   #ifdef CONFIG_SHADOW_CALL_STACK
>   	void			*scs_base;


Great, that now fits into a cacheline. I guess other structures would 
deserve the same attention.

You can add:

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

Thanks,

Alex