HT vs non HT Cpu...

[Blitz Blitz]

Hi. Just interesting what cpus is better, - with HT or without HT(hyperthreading)? I somewhere read that hyperthreading produce more heat? Maybe i5 is better and runs cooler, than i7? What cooler need to use, and what temps is optimal for cpu performance and longevity?

 

[InvalidError]

Between two CPUs with the same core count based on the same architecture, multi-threading adds 20-40% more performance in software that can make use of the extra threads. Power-wise, it only uses ~10% more power.

 

[Solandri]

As stated above, it adds about 30% more performance to software which works well with hyperthreaading. The problem is only a limited amount of software falls into this category. Mostly it's video encoding, data compression, and encryption/decryption. There are a handful of games which are optimized to use HT well too.

HT relies on using parts of a CPU core which aren't being used, so requires the software be pegging the CPU at 100% while performing a wide variety of different tasks. Most software which pegs the CPU at 100% does so because it's trying to rapidly perform a single task, and so see little to no benefit from HT because the parts of the physical cores needed for that task are already being used, and thus unavailable in the virtual cores. A few poorly threaded programs can even run slower with HT (a crucial thread gets assigned to a virtual core instead of a real one, causing other threads which rely on it to have to wait - a condition called blocking).

I usually disable HT on my i7 quad core laptop to eek out about 20-30 min more battery life and to reduce the heat when I use it on my lap. I find the performance increase HT offers to be almost negligible in most of what I do. If you do video encoding or a lot of data compression and/or encryption, then by all means I recommend the i7. If you're unsure and rich, then get the i7 - you can always disable HT like I do if the heat becomes a problem. If you do a lot of number crunching or data analysis, I also recommend the i7 simply because of its larger L3 cache. But for the vast majority of people, I consider the i5 more than enough. Especially if you're comparing one of the new hexacore i5s (Coffee Lake - 6 physical cores) to an older quad core i7 (4 physical cores + HT becomes effectively only 5.2 cores on programs which work well with HT).