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

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Date:	Mon, 12 Oct 2015 20:08:48 +0200
From:	christophe leroy <christophe.leroy@....fr>
To:	Scott Wood <scottwood@...escale.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 22/25] powerpc32: move xxxxx_dcache_range() functions
 inline



Le 08/10/2015 21:12, Scott Wood a écrit :
> On Wed, 2015-10-07 at 14:49 +0200, Christophe Leroy wrote:
>> Le 29/09/2015 02:29, Scott Wood a écrit :
>>> On Tue, Sep 22, 2015 at 06:51:13PM +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 */
>>>> +}
>>> I know this is 32-bit-specific code, but it's still bad practice to use
>>> "unsigned int" for addresses or sizes thereof.
>>>
>>>
>> Ok, I can fix size, but what about start and stop ? If I change that, it
>> means I also have to fix all caller. Do you expect me to do that ?
> start and stop are already unsigned long.
>
>> And it is very unlykely, but what if for some reason someone wants to
>> invalidate the entire user address space which is 3Gbytes size ? A
>> signed size would be negative here.
> Why would size be signed?

Oops, indeed I misunderstood your comment, thought you said:
* size has to be signed int instead of unsigned int
* addresses have to be void *

I understand now that size and addresses should be unsigned long instead

Christophe


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