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SubjectRe: [PATCH 3/4] powerpc32: memset(0): use cacheable_memzero


Le 14/05/2015 02:55, Scott Wood a écrit :
> On Tue, 2015-05-12 at 15:32 +0200, Christophe Leroy wrote:
>> cacheable_memzero uses dcbz instruction and is more efficient than
>> memset(0) when the destination is in RAM
>>
>> This patch renames memset as generic_memset, and defines memset
>> as a prolog to cacheable_memzero. This prolog checks if the byte
>> to set is 0 and if the buffer is in RAM. If not, it falls back to
>> generic_memcpy()
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>> ---
>> arch/powerpc/lib/copy_32.S | 15 ++++++++++++++-
>> 1 file changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/lib/copy_32.S b/arch/powerpc/lib/copy_32.S
>> index cbca76c..d8a9a86 100644
>> --- a/arch/powerpc/lib/copy_32.S
>> +++ b/arch/powerpc/lib/copy_32.S
>> @@ -12,6 +12,7 @@
>> #include <asm/cache.h>
>> #include <asm/errno.h>
>> #include <asm/ppc_asm.h>
>> +#include <asm/page.h>
>>
>> #define COPY_16_BYTES \
>> lwz r7,4(r4); \
>> @@ -74,6 +75,18 @@ CACHELINE_MASK = (L1_CACHE_BYTES-1)
>> * to set them to zero. This requires that the destination
>> * area is cacheable. -- paulus
>> */
>> +_GLOBAL(memset)
>> + cmplwi r4,0
>> + bne- generic_memset
>> + cmplwi r5,L1_CACHE_BYTES
>> + blt- generic_memset
>> + lis r8,max_pfn@ha
>> + lwz r8,max_pfn@l(r8)
>> + tophys (r9,r3)
>> + srwi r9,r9,PAGE_SHIFT
>> + cmplw r9,r8
>> + bge- generic_memset
>> + mr r4,r5
> max_pfn includes highmem, and tophys only works on normal kernel
> addresses.
Is there any other simple way to determine whether an address is in RAM
or not ?

I did that because of the below function from mm/mem.c

|int page_is_ram(unsigned long pfn)
{
#ifndef CONFIG_PPC64 /* XXX for now */
return pfn< max_pfn;
#else
unsigned long paddr= (pfn<< PAGE_SHIFT);
struct memblock_region*reg;

for_each_memblock(memory, reg)
if (paddr>= reg->base&& paddr< (reg->base+ reg->size))
return 1;
return 0;
#endif
}
|



>
> If we were to point memset_io, memcpy_toio, etc. at noncacheable
> versions, are there any other callers left that can reasonably point at
> uncacheable memory?
Do you mean we could just consider that memcpy() and memset() are called
only with destination on RAM and thus we could avoid the check ?
copy_tofrom_user() already does this assumption (allthought a user app
could possibly provide a buffer located in an ALSA mapped IO area)

Christophe


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