undefined | Better HN

0 pointszrm6y ago0 comments

Are you measuring actual performance though or just IPC?

We know Intel has that problem with AVX-512. You can get a lot of throughput per cycle with those instructions but the cost is they cause the processor to run hot and have to downclock. It's possible (and really expected) that the same thing happens to some extent at unusually high IPC. Getting 15% higher IPC doesn't really buy you anything if the processor has to lower its clock speed by 15% to execute that type of code.

0 comments

3 comments · 1 top-level

jdsully6y ago· 2 in thread

Actual wallclock time. The code is 100% scalar - LZF is very byte oriented and I haven't found a good way to vectorize it. IPC counts were used to help guide tuning but not a determination of success.

I don't really understand why people think this is controversial. Somehow an Intel cpu on a generation behind process is still competitive with a 7nm CPU with more cache. Intel must have one hell of an architecture to make that possible. AMD did a good job for the most common workloads but they have work to do with Zen3 if they want to maintain that lead when Intel finally figures out its manufacturing.

zrmOP6y ago

Have you looked at what 7zip is doing? That should be a similar type of code and it runs very well on Zen2.

jdsully6y ago

7zip doesn't use LZF. LZF is mandated by the file format I'm working with.

j / k navigate · click thread line to collapse