On Nov 16, 2009, at 2:07 PM, Satish Balay wrote:

The whole reason for having PetscMalloc2() PetscMalloc3() etc is to reduce the number of calls to malloc() - thus hoping for a performance boost.

For one - this usage was triggered by old SunOS boxes [where malloc took a long time]. We don't know if this is still true for any of the current OSes.

With the increased complexity of managing alignment here - is it still worth keeping these merged mallocs? [do we still get any payoff from this complexity? - instead of relying directly on malloc() for the necessary alignment?]

I would argue yes. Not only is there the issue of improved performance of the malloc but it also is a nice way to have clarity in the code as to what allocated arrays are associated together. Barry

I'm not sure..

Satish

On Mon, 16 Nov 2009, Jed Brown wrote:

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Barry Smith wrote:

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Agreed this would be a good option to have. The question is how to do it without having a morass of nasty nested if-defs. Note that portably getting alignment out of malloc() alone is already ugly and not as simple a code as I would like.

To simplify things we could always require 16 byte alignment everywhere? But is that a desirable?

I doubt it's harmful, I don't think I understand where the nested ifdefs come in. The required alignment only needs to be stated in one place, I have something like the following in one of my projects.

/* current */ #define PetscMalloc3(m1,t1,r1,m2,t2,r2,m3,t3,r3) \ (PetscMalloc((m1)*sizeof(t1)+(m2)*sizeof(t2)+ (m3)*sizeof(t3),r1) \ || (*(r2) = (t2*) (*(r1)+m1), \ *(r3) = (t3*)(*(r2)+m2),0))

/* aligned */ #define PetscMalloc3(m1,t1,r1,m2,t2,r2,m3,t3,r3) \ (PetscMalloc((m1)*sizeof(t1)+(m2)*sizeof(t2)+ (m3)*sizeof(t3)+2*(PETSC_MEMALIGN-1),r1) \ || (*(r2) = (t2*)PETSC_ALIGN(*(r1)+m1), \ *(r3) = (t3*)PETSC_ALIGN(*(r2)+m2),0))

#define PETSC_ALIGN(p) PetscNextAligned((uintptr_t) (p),PETSC_MEMALIGN-1)

static inline void *PetscNextAligned(uintptr_t base,uintptr_t mask) {return (void*)((base + mask) & ~mask);}

Note that this is a no-op if PETSC_MEMALIGN=1 and thus compiles to exactly what we have now.

Jed