linux-kernel - Re: [PATCH v2 22/25] powerpc32: move xxxxx_dcache

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Date:	Tue, 22 Sep 2015 18:12:27 +0000
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	"christophe.leroy@....fr" <christophe.leroy@....fr>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"mpe@...erman.id.au" <mpe@...erman.id.au>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"scottwood@...escale.com" <scottwood@...escale.com>
CC:	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 22/25] powerpc32: move xxxxx_dcache_range() functions
 inline

On Tue, 2015-09-22 at 18:51 +0200, Christophe Leroy wrote:
> flush/clean/invalidate _dcache_range() functions are all very
> similar and are quite short. They are mainly used in __dma_sync()
> perf_event locate them in the top 3 consumming functions during
> heavy ethernet activity
> 
> They are good candidate for inlining, as __dma_sync() does
> almost nothing but calling them
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
> New in v2
> 
>  arch/powerpc/include/asm/cacheflush.h | 55 +++++++++++++++++++++++++++--
>  arch/powerpc/kernel/misc_32.S         | 65 -----------------------------------
>  arch/powerpc/kernel/ppc_ksyms.c       |  2 ++
>  3 files changed, 54 insertions(+), 68 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/cacheflush.h b/arch/powerpc/include/asm/cacheflush.h
> index 6229e6b..6169604 100644
> --- a/arch/powerpc/include/asm/cacheflush.h
> +++ b/arch/powerpc/include/asm/cacheflush.h
> @@ -47,12 +47,61 @@ static inline void __flush_dcache_icache_phys(unsigned long physaddr)
>  }
>  #endif
>  
> -extern void flush_dcache_range(unsigned long start, unsigned long stop);
>  #ifdef CONFIG_PPC32
> -extern void clean_dcache_range(unsigned long start, unsigned long stop);
> -extern void invalidate_dcache_range(unsigned long start, unsigned long stop);
> +/*
> + * Write any modified data cache blocks out to memory and invalidate them.
> + * Does not invalidate the corresponding instruction cache blocks.
> + */
> +static inline void flush_dcache_range(unsigned long start, unsigned long stop)
> +{
> +	void *addr = (void *)(start & ~(L1_CACHE_BYTES - 1));
> +	unsigned int size = stop - (unsigned long)addr + (L1_CACHE_BYTES - 1);
> +	unsigned int i;
> +
> +	for (i = 0; i < size >> L1_CACHE_SHIFT; i++, addr += L1_CACHE_BYTES)
> +		dcbf(addr);
> +	if (i)
> +		mb();	/* sync */
> +}

This feels optimized for the uncommon case when there is no invalidation.
I THINK it would be better to bail early and use do { .. } while(--i); instead.

 Jocke--
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