Author vstinner
Recipients benjamin.peterson, neologix, njs, pitrou, rhettinger, skrah, tim.peters, trent, vstinner, wscullin, xdegaye
Date 2017-10-31.14:23:42
SpamBayes Score -1.0
Marked as misclassified Yes
Message-id <1509459822.23.0.213398074469.issue18835@psf.upfronthosting.co.za>
In-reply-to
Content
Nathaniel Smith: "Given the complexities here, and that the Track/Untrack functions are public now, I do wonder if the actual aligned allocation routines should just be an internal API (i.e., not exposed in Python.h)."

I don't see why we would hide PyMem_AlignedAlloc() but requires to implement aligned_alloc in PyMem_SetAllocators().

The plan is also to slowly use PyMem_AlignedAlloc() internally for performance.

Can you elaborate the "complexities"? Do you mean that the proposed PyMem_AlignedAlloc() API is more complex than calling directly posix_memalign()?

PyMem_AlignedAlloc() is designed for performance. For best performances, CPUs require memory to be aligned on convenient values like powers of 2 ;-) I also understand that alignment must be a multiple of sizeof(void*) because CPU work on "CPU words". On a 64-bit CPU, a word is 8 bytes. If the memory is aligned on 4 bytes, it may have to fetch two words, you loose the advantage of memory alignment.

I understand that PyMem_AlignedAlloc() requirements come from the CPU arhcitecture, it's not an arbitrary limitation just for the fun ;-)
History
Date User Action Args
2017-10-31 14:23:42vstinnersetrecipients: + vstinner, tim.peters, rhettinger, pitrou, benjamin.peterson, trent, njs, skrah, neologix, xdegaye, wscullin
2017-10-31 14:23:42vstinnersetmessageid: <1509459822.23.0.213398074469.issue18835@psf.upfronthosting.co.za>
2017-10-31 14:23:42vstinnerlinkissue18835 messages
2017-10-31 14:23:42vstinnercreate