[Someone1234]

Ouch. I will say though, Hyper-Threading is a lot less valuable these days than it was when it was first introduced (except for the few dual core CPUs still available).

When you have four-six-eight or more cores, there's less value in doubling that number. The gain is lower.

[hermitdev]

Except the performance of hyper-threading today is far better than it was first introduced. I had a dual-socket P4 Xeon box w/ HT around 2003. Single-threaded performance with HT enabled was around 70% of what it was with HT disabled. Today, I think you'd see only about 95-98% of enabled vs disabled performance.

I don't have hard numbers to back this up, it's purely my personal experience/recollection. On my 2 socket P4 Xeon box, I disabled HT. On my current I7 6-core box, I have HT on.

[derekp7]

On the other side, a hyperthreaded CPU used to be about 10 - 30% gain, but in tests I've ran on recent hardware (HP DL380 Gen 10) hyperthreading gives around 70% more performance (the test I used was running pigz [parallel gzip] on a large file).

[greglindahl]

That's a great example of how hyperthreading's performance effects are extremely workload dependent.

[moab]

It's still important to hide latency and saturate the memory controllers for programs with irregular memory accesses (e.g. graph algorithms), although the difference is not 2x, but something more like 10-15% over running without hyper-threading.

[garganzol]

Depends on load. I run parallel integration tests on hyper-threaded machines and usually see 80% gains.