linux-kernel - Re: [PATCH] MIPS: Take in account load hazards for HI/LO restoring

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Message-ID: <Zi9X8cqTpWUR1Z6l@alpha.franken.de>
Date: Mon, 29 Apr 2024 10:18:57 +0200
From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To: Siarhei Volkau <lis8215@...il.com>
Cc: linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
	Paul Cercueil <paul@...pouillou.net>
Subject: Re: [PATCH] MIPS: Take in account load hazards for HI/LO restoring

On Thu, Oct 12, 2023 at 07:20:27PM +0300, Siarhei Volkau wrote:
> MIPS CPUs usually have 1 to 4 cycles load hazards, thus doing load
> and right after move to HI/LO will usually stall the pipeline for
> significant amount of time. Let's take it into account and separate
> loads and mthi/lo in instruction sequence.
> 
> The patch uses t6 and t7 registers as temporaries in addition to t8.
> 
> The patch tries to deal with SmartMIPS, but I know little about and
> haven't tested it.
> 
> Signed-off-by: Siarhei Volkau <lis8215@...il.com>
> ---
>  arch/mips/include/asm/stackframe.h | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/mips/include/asm/stackframe.h b/arch/mips/include/asm/stackframe.h
> index a8705aef47e1..3821d91b00fd 100644
> --- a/arch/mips/include/asm/stackframe.h
> +++ b/arch/mips/include/asm/stackframe.h
> @@ -308,17 +308,11 @@
>  		jal	octeon_mult_restore
>  #endif
>  #ifdef CONFIG_CPU_HAS_SMARTMIPS
> -		LONG_L	$24, PT_ACX(sp)
> -		mtlhx	$24
> -		LONG_L	$24, PT_HI(sp)
> -		mtlhx	$24
> -		LONG_L	$24, PT_LO(sp)
> -		mtlhx	$24
> -#elif !defined(CONFIG_CPU_MIPSR6)
> +		LONG_L	$14, PT_ACX(sp)
> +#endif
> +#if defined(CONFIG_CPU_HAS_SMARTMIPS) || !defined(CONFIG_CPU_MIPSR6)

isn't that just #ifndef CONFIG_CPU_MIPSR6 ? 

Thomas.

-- 
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