On Thu, 2015-05-14 at 10:50 +0200, christophe leroy wrote:
>
> 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.le...@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 ?
If you want to do it based on the virtual address, rather than doing a
tablewalk or TLB search, you need to limit it to lowmem.
> 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
> }
Right, the problem is figuring out the pfn in the first place.
> > 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 ?
Maybe. If that's not a safe assumption I hope someone will point it
out.
> copy_tofrom_user() already does this assumption (allthought a user app
> could possibly provide a buffer located in an ALSA mapped IO area)
The user could also pass in NULL. That's what the fixups are for. :-)
-Scott
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