The Disappointing Direction Of Linux Performance From 4.16 To 5.4 Kernels

[Azrael5]

Don't rant: read and understand. The slowdown is largely due to hardware security mitigations, which you can turn off.

I know. It's hardware flaws. So the question is if free-bugs Cpus are affected by mitigation as well.

[pgoetz]

I am not saying it has been done, but it is most certainly POSSIBLE. That fact alone should give you pause. You folks disabling mitigations and other security features are nuts.

Hard to exploit vulnerabilities that have been exploited stay private. Quite often, only your data or access to your machine is sold or used fore nefarious purposes, not the vulnerability itself.

A lot of my systems are

1. Used for lengthy scientific computations
2. Behind a firewall
3. Are only accessible by trusted users, mostly scientists who both know nothing about hacking and don't care

I can't think of any reason why I wouldn't disable mitigations on these systems.

[pgoetz]

I know. It's hardware flaws. So the question is if free-bugs Cpus are affected by mitigation as well.

I'm not sure, but who has bug-free CPUs? AFAIK, the Intel vulnerabilities go back years and affect multiple generations of CPUs.

[skeevy420]

I'm not sure, but who has bug-free CPUs? AFAIK, the Intel vulnerabilities go back years and affect multiple generations of CPUs.

Cylons.

[tytso]

FWIW, I wasn't able to replicate the performance delta using upstream kernels, running on a Google Compute Engine VM, machtype n1-highcpu-8, using a GCE Local SSD (SCSI-attached) for the first benchmark, which I believe was the pts/sqlite benchmark using a thread count of 1:

SQLite 3.30.1
Threads / Copies: 1
Seconds < Lower Is Better
5.4.0-rc3 ................. 224 |==========================================
5.3.0 ..................... 225 |===========================================
v5.4-rc3-80-gafb2442fa429 . 227 |===========================================
5.4.0-rc7 ................. 223 |==========================================

Processor: Intel Xeon (4 Cores / 8 Threads), Chipset: Intel 440FX 82441FX PMC, Memory: 1 x 7373 MB RAM, Disk: 11GB PersistentDisk + 403GB EphemeralDisk, Network: Red Hat Virtio device

OS: Debian 10, Kernel: 5.4.0-rc3-xfstests (x86_64) 20191113, Compiler: GCC 8.3.0, File-System: ext4, System Layer: KVM

[Azrael5]

I'm not sure, but who has bug-free CPUs? AFAIK, the Intel vulnerabilities go back years and affect multiple generations of CPUs.

Some kind of Arm Cpus are free from the known bugs.

[starshipeleven]

I know. It's hardware flaws. So the question is if free-bugs Cpus are affected by mitigation as well.

No, mitigations are turned off for those CPUs.
For example Meltdown mitigation is turned off for AMD CPUs that are not affected.

[starshipeleven]

Cylons.

That's debatable. They wanted to kill everyone