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My server's 'dedicated' CPU is oversubscribed

Dedicated Servers by annexbi 6 replies 445 views
#1

So I signed up with Contabo (you know the one) for their "dedicated CPU" plan six months ago (or was it seven? Time blurs when you're debugging at 3am) and everything seemed fine (if you call "fine" a baseline that wobbles like a jelly on a washing machine) until I started running actual benchmarks for a client project (the kind where you need reproducible numbers, not lottery results).

Here's the smoking gun. [code]Run 1: sysbench cpu 1834 events/sec
Run 2: sysbench cpu 947 events/sec
Run 3: sysbench cpu 2102 events/sec
Run 4: sysbench cpu 891 events/sec

That variance (if you can call a 2.3x spread "variance" and not "someone else's cryptocurrency operation next door") is not silicon lottery. That's neighbor noise. I opened a ticket (politely! I was polite! My mother raised me right) and after three weeks of "our technicians are investigating" they admitted (in writing, which I screenshot, because of course I did) that "dedicated" on their platform means "dedicated thread on a shared core" (their words, not mine (though I wish I'd coined something that brazen)).

I migrated to InterServer (true dedicated, verified with lscpu showing physical cores I can actually touch (metaphorically)) at roughly 40% premium. Here's the after: [code]Run 1: sysbench cpu 2847 events/sec
Run 2: sysbench cpu 2833 events/sec
Run 3: sysbench cpu 2851 events/sec
Run 4: sysbench cpu 2845 events/sec

Standard deviation under 0.4%. That's what dedicated means. That's what I paid for. Consider this a warning (a polite one (naturally)).

push. done. coffee.
#2
annexbi said:
I screenshot, because of course I did

Good instinct. Screenshots are evidence!

What concerns me more: how many "dedicated" plans out there are pulling this thread-sharing trick? You verified with lscpu which is smart but most users won't. Could go wrong: provider silently migrates you to noisier neighbor after signup. Could go wrong: they throttle your "dedicated" core during their peak. Could go wrong: your benchmark data ends up in their marketing as "typical performance."

Install fail2ban immediately on the new box by the way. Fresh server, fresh attack surface.

airgapped, encrypted, faraday'd, still worried
#3

Oh noooo annexbi I have make exactly the same experience with OVHcloud since 2 days I have open a ticket lol they say "we will check"

Your numbers are very impressive after migration, it is possible to do that with all provider? I think I will change also but the price... Franchement 40% more is hard for my budget

Can I ask how many time the migration take you? I have 3 tb of data lol

Vive la résistance... électrique
9 #4
lucgone said:
How many time the migration take

So the Data Transfer itself is not the Problem, the Verification is what kills your Weekend. Na yes.

I had a similar Situation with Hetzner last year. Their "Dedicated vCPU" turned out to be a Hyperthread with a fancy Label. The Performance Penalty for my Kubernetes Workloads was gemütlich only if you find 40% slower Pod Scheduling cozy.

So my Advice: check /proc/cpuinfo for "core id" versus "physical id" Mismatches. If the Numbers overlap, you are sharing Silicon. The true dedicated Server will show distinct physical Cores with no Overlap.

#5

Hey folks, marcus from InterServer here

Just wanna say: anne's numbers check out, we verified that box ourselves. Super stoked you took the time to post this, gonna share it with our onboarding team as a case study (with your permission, hit me up).

Also gonna be real with you: we used to offer "budget dedicated" that was thread-shared. Killed it last year. Wasn't worth the reputation hit. Some lessons you learn the hard way

@annexbi if you ever need a hand tuning that workload, ping me direct. We messed up early on, fixing it fast is all we can do.

42U and still growing
#6

Which kernel version on the Contabo box before migration

#7

How much RAM on the oversubscribed plan

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