linux-kernel - Re: [PATCH] ARC: Allow disabling of prefetch operations for debugging purposes

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Message-ID: <ce12fd9c-d2df-2d3d-5bfd-1cc1e73c8f64@synopsys.com>
Date:   Thu, 18 Jan 2018 10:48:08 -0800
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARC: Allow disabling of prefetch operations for debugging
 purposes

On 01/18/2018 05:48 AM, Alexey Brodkin wrote:
> Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
> ---
>   arch/arc/Kconfig                 |  5 +++++
>   arch/arc/include/asm/processor.h | 11 +++++++++++
>   arch/arc/lib/memcpy-archs.S      | 16 ++++++++++++++++
>   arch/arc/lib/memset-archs.S      |  6 ++++++
>   4 files changed, 38 insertions(+)
>
> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> index 9d5fd00d9e91..aa5262e8e43f 100644
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -532,6 +532,11 @@ config ARC_DBG_TLB_PARANOIA
>   	bool "Paranoia Checks in Low Level TLB Handlers"
>   	default n
>   
> +config ARC_DISABLE_PREFETCH
> +	bool "Disable use of prefetch instructions"
> +	default n
> +	help
> +	  Suppresses usage of prefetchw and prealloc instructions.
>   endif
>   
>   config ARC_UBOOT_SUPPORT
> diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h
> index 8ee41e988169..01011c0515d4 100644
> --- a/arch/arc/include/asm/processor.h
> +++ b/arch/arc/include/asm/processor.h
> @@ -106,6 +106,17 @@ extern unsigned int get_wchan(struct task_struct *p);
>    */
>   #define current_text_addr() ({ __label__ _l; _l: &&_l; })
>   
> +#ifdef CONFIG_ARC_DISABLE_PREFETCH
> +#define ARCH_HAS_PREFETCH
> +#define prefetch(x)
> +
> +#define ARCH_HAS_PREFETCHW
> +#define prefetchw(x)
> +
> +#define ARCH_HAS_SPINLOCK_PREFETCH
> +#define spin_lock_prefetch(x)
> +#endif /* CONFIG_ARC_DISABLE_PREFETCH */
> +
>   #endif /* !__ASSEMBLY__ */
>   
>   /*
> diff --git a/arch/arc/lib/memcpy-archs.S b/arch/arc/lib/memcpy-archs.S
> index d61044dd8b58..0a29d024be01 100644
> --- a/arch/arc/lib/memcpy-archs.S
> +++ b/arch/arc/lib/memcpy-archs.S
> @@ -41,8 +41,10 @@
>   #endif
>   
>   ENTRY_CFI(memcpy)
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetch [r1]		; Prefetch the read location
>   	prefetchw [r0]		; Prefetch the write location
> +#endif

This code is already unreadable and this change is not helping. Can we make some 
macros "C" / gas style and have the switch inside the macro rather than littering 
this all over the place please !

>   	mov.f	0, r2
>   ;;; if size is zero
>   	jz.d	[blink]
> @@ -72,8 +74,10 @@ ENTRY_CFI(memcpy)
>   	lpnz	@.Lcopy32_64bytes
>   	;; LOOP START
>   	LOADX (r6, r1)
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	PREFETCH_READ (r1)
>   	PREFETCH_WRITE (r3)
> +#endif
>   	LOADX (r8, r1)
>   	LOADX (r10, r1)
>   	LOADX (r4, r1)
> @@ -117,9 +121,13 @@ ENTRY_CFI(memcpy)
>   	lpnz	@.Lcopy8bytes_1
>   	;; LOOP START
>   	ld.ab	r6, [r1, 4]
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetch [r1, 28]	;Prefetch the next read location
> +#endif
>   	ld.ab	r8, [r1,4]
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetchw [r3, 32]	;Prefetch the next write location
> +#endif
>   
>   	SHIFT_1	(r7, r6, 24)
>   	or	r7, r7, r5
> @@ -162,9 +170,13 @@ ENTRY_CFI(memcpy)
>   	lpnz	@.Lcopy8bytes_2
>   	;; LOOP START
>   	ld.ab	r6, [r1, 4]
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetch [r1, 28]	;Prefetch the next read location
> +#endif
>   	ld.ab	r8, [r1,4]
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetchw [r3, 32]	;Prefetch the next write location
> +#endif
>   
>   	SHIFT_1	(r7, r6, 16)
>   	or	r7, r7, r5
> @@ -204,9 +216,13 @@ ENTRY_CFI(memcpy)
>   	lpnz	@.Lcopy8bytes_3
>   	;; LOOP START
>   	ld.ab	r6, [r1, 4]
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetch [r1, 28]	;Prefetch the next read location
> +#endif
>   	ld.ab	r8, [r1,4]
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetchw [r3, 32]	;Prefetch the next write location
> +#endif
>   
>   	SHIFT_1	(r7, r6, 8)
>   	or	r7, r7, r5
> diff --git a/arch/arc/lib/memset-archs.S b/arch/arc/lib/memset-archs.S
> index 62ad4bcb841a..343f292d92a0 100644
> --- a/arch/arc/lib/memset-archs.S
> +++ b/arch/arc/lib/memset-archs.S
> @@ -11,7 +11,9 @@
>   #undef PREALLOC_NOT_AVAIL
>   
>   ENTRY_CFI(memset)
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetchw [r0]		; Prefetch the write location
> +#endif
>   	mov.f	0, r2
>   ;;; if size is zero
>   	jz.d	[blink]
> @@ -48,11 +50,13 @@ ENTRY_CFI(memset)
>   
>   	lpnz	@.Lset64bytes
>   	;; LOOP START
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   #ifdef PREALLOC_NOT_AVAIL
>   	prefetchw [r3, 64]	;Prefetch the next write location
>   #else
>   	prealloc  [r3, 64]
>   #endif
> +#endif /* CONFIG_ARC_DISABLE_PREFETCH */
>   #ifdef CONFIG_ARC_HAS_LL64
>   	std.ab	r4, [r3, 8]
>   	std.ab	r4, [r3, 8]
> @@ -85,7 +89,9 @@ ENTRY_CFI(memset)
>   	lsr.f	lp_count, r2, 5 ;Last remaining  max 124 bytes
>   	lpnz	.Lset32bytes
>   	;; LOOP START
> +#ifndef CONFIG_ARC_DISABLE_PREFETCH
>   	prefetchw   [r3, 32]	;Prefetch the next write location
> +#endif
>   #ifdef CONFIG_ARC_HAS_LL64
>   	std.ab	r4, [r3, 8]
>   	std.ab	r4, [r3, 8]