On Jun 10, 2009, at 1:58 PM, David Bergman wrote:
On Jun 10, 2009, at 1:49 PM, David Bergman wrote:
On Jun 10, 2009, at 4:54 AM, Christian Schladetsch wrote:
Hi Artyom,
You **must** return aligned pointers from allocators.
boost::monotonic does not allocate.
I wonder what that 'allocator' of yours is for then? ;-)
Of course it allocates. And you fail to align the start address, which makes certain use cases crash on certain platforms. On Intel, it "just" gives the user a worse performance when misaligned. This is not aligned (pun intended...) with your overall goal to give the developer a high-performance tool. But do not take my word for it, I ran a test with your container, the attached sample program and got around 33.3 picoseconds on average to perform an increment on an aligned long compared to 35.6 picoseconds for a misaligned long, i.e., some 8% difference. Actually, I got a bit more with other operations.
In fact, the attached version is a very lenient one, since it does give proper alignment for a lot of iterations... I used prime number distributions in other samples. Nevertheless, this sample produced between 8% and 10% difference between the two cases. I can provide you with more information about the performance hit of using misaligned stuff if you want.
When packing the structures, such as with __attribute((__packed__)) for GCC, I got an almost 20% speed penalty on my Intel-based OS X laptop, when using your non-aligning allocator. /David