24-May-2013 09:02, Manu пишет:
On 24 May 2013 14:11, Marco Leise <marco.le...@gmx.de <mailto:marco.le...@gmx.de>> wrote:Am Thu, 23 May 2013 20:21:47 -0400 schrieb "Jonathan M Davis" <jmdavisp...@gmx.com <mailto:jmdavisp...@gmx.com>>: > At some point, we're probably going to need to > benchmark stuff more agressively and optimize Phobos in general more, because > it's the standard library. And eliminating unnecessary memory allocations > definitely goes along with that. > > - Jonathan M Davis On a related note, a while back I benchmarked the naive Phobos approach to create a Windows API (wchar) string from a D string with using alloca to convert the string on a piece of stack memory like this: http://dpaste.1azy.net/b60d37d4 IIRC it was 13(!) times faster for ~100 chars of English text and 5 times for some multi-byte characters. I think this approach is too hackish for Phobos, but it demonstrates that there is much room. I don't think it's hack-ish at all, that's precisely what the stack is there for. It would be awesome for people to use alloca in places that it makes sense. Especially in cases where the function is a leaf or leaf-stem (ie, if there is no possibility of recursion), then using the stack should be encouraged. For safety, obviously phobos should do something like: void[] buffer = bytes < reasonable_anticipated_buffer_size ? alloca(bytes) : new void[bytes]; toStringz is a very common source of allocations. This alloca approach would be great in those cases, filenames in particular.
Alternatively just make a TLS buffer as scratchpad and use that everywhere. -- Dmitry Olshansky
