From: Michael Ellerman <mpe@ellerman•id.au>
To: Christophe Leroy <christophe.leroy@csgroup•eu>,
Benjamin Herrenschmidt <benh@kernel•crashing.org>,
Paul Mackerras <paulus@samba•org>
Cc: linuxppc-dev@lists•ozlabs.org, linux-kernel@vger•kernel.org
Subject: Re: [PATCH] powerpc: Redefine HMT_xxx macros as empty on PPC32
Date: Thu, 26 Aug 2021 14:57:42 +1000 [thread overview]
Message-ID: <878s0oby61.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <c5a07fadea33d640ad10cecf0ac8faaec1c524e0.1629898474.git.christophe.leroy@csgroup.eu>
Christophe Leroy <christophe.leroy@csgroup•eu> writes:
> HMT_xxx macros are macros for adjusting thread priority
> (hardware multi-threading) are macros inherited from PPC64
> via commit 5f7c690728ac ("[PATCH] powerpc: Merged ppc_asm.h")
>
> Those instructions are pointless on PPC32, but some common
> fonctions like arch_cpu_idle() use them.
>
> So make them empty on PPC32 to avoid those instructions.
I guess we're pretty sure no 32-bit CPUs do anything with those.
e6500 can run in 32-bit mode, and is 2-way threaded AIUI, so it's
*possible* it could use them.
But I can't find any mention of those special nops in the e6500 core
manual. And actually it does have documentation about thread priority
registers, PPR32, TPRI0/1, but it says they're not used in e6500.
So I guess this seems safe, I'll pick it up.
cheers
> diff --git a/arch/powerpc/include/asm/vdso/processor.h b/arch/powerpc/include/asm/vdso/processor.h
> index e072577bc7c0..8d79f994b4aa 100644
> --- a/arch/powerpc/include/asm/vdso/processor.h
> +++ b/arch/powerpc/include/asm/vdso/processor.h
> @@ -5,12 +5,21 @@
> #ifndef __ASSEMBLY__
>
> /* Macros for adjusting thread priority (hardware multi-threading) */
> +#ifdef CONFIG_PPC64
> #define HMT_very_low() asm volatile("or 31, 31, 31 # very low priority")
> #define HMT_low() asm volatile("or 1, 1, 1 # low priority")
> #define HMT_medium_low() asm volatile("or 6, 6, 6 # medium low priority")
> #define HMT_medium() asm volatile("or 2, 2, 2 # medium priority")
> #define HMT_medium_high() asm volatile("or 5, 5, 5 # medium high priority")
> #define HMT_high() asm volatile("or 3, 3, 3 # high priority")
> +#else
> +#define HMT_very_low()
> +#define HMT_low()
> +#define HMT_medium_low()
> +#define HMT_medium()
> +#define HMT_medium_high()
> +#define HMT_high()
> +#endif
>
> #ifdef CONFIG_PPC64
> #define cpu_relax() do { HMT_low(); HMT_medium(); barrier(); } while (0)
> --
> 2.25.0
next prev parent reply other threads:[~2021-08-26 4:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-25 13:34 [PATCH] powerpc: Redefine HMT_xxx macros as empty on PPC32 Christophe Leroy
2021-08-26 4:57 ` Michael Ellerman [this message]
2021-08-31 13:56 ` Michael Ellerman
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