htop CPU graph doesn't match numbers

[Elliott]

I am trying to improve Samba performance on a server with 40GbE. Samba server is single threaded, so htop shows it pegged at 100%. But why do the bar graphs at the top show differently? I would expect one core to pe pegged at 100%.

 

[PacketMan]

I really don't know the true answer to this, but based on observations I have come to the conclusion that FreeBSD (and likely many other OSs) flip the process threads around on the CPU cores. So for a few cycles its on one core, then another, then another, etc. Since top shows you an interval, you will likely never see a cpu core at 100% with all others at 0%. That is my guess.

Why heat up one core super hot with the rest being cool? Spread the heat around I say.

Now we wait for the real answer. ?

 

[Elliott]

Good guess, but yes>/dev/null & stays on one core so what's the difference?
I believe moving between cores would create some unnecessary latency. Whether this is actually noticeable I don't know. But some modern CPUs use Turbo Boost to overclock one core, so this could have a significant performance impact.