H.J. Lu wrote:
> You can use __BIGGEST_ALIGNMENT__ for that purpose.
Yes, _for that purpose_ it works perfectly. However, I would
also like be able to align fields to cache line size. I have a set
of C++ template cache geometry descriptors which provide
a constant by the name of line_size:
namespace cache {
template <std::size_t N_level> class geometry;
// ---------------
template <> class geometry<1> : private nonconstructible {
// Superclass
typedef nonconstructible super;
public:
static const std::size_t capacity = 32 * 1024;
static const std::size_t associativity = 8;
static const std::size_t line_size = 64;
};
// ---------------
template <> class geometry<2> : private nonconstructible {
// Superclass
typedef nonconstructible super;
public:
static const std::size_t capacity = 3 * 1024 * 1024;
static const std::size_t associativity = 12;
static const std::size_t line_size = 64;
};
}
I would like to declare a level 1 data cache line size-aligned variable x:
int x __attribute__((__aligned__(cache::geometry<1>::line_size)));
which is not possible now. BTW, since GCC has -mtune=native, it
would be great to have a compiler-provided cache info in the form
of a bunch of target-dependent preprocessor definitions, e.g. for Core2:
__GCC_DCACHE_LEVELS 2
__GCC_ICACHE_LEVELS 2
__GCC_DCACHE_LINE_SIZE1 64
__GCC_DCACHE_LINE_SIZE2 64
__GCC_DCACHE_ASSOCIATIVITY1 8
__GCC_DCACHE_ASSOCIATIVITY2 12
etc. It would help in a lot of cases, e.g. lock-free algorithms, false
sharing avoidance, alignment calculations in custom allocators etc.
Best regards,
Piotr Wyderski
