Re: Ars claims: Fedora 32 is sluggish

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On Thu, Feb 11, 2021 at 10:14 AM Viktor Ashirov <vashirov@xxxxxxxxxx> wrote:
> On Wed, Feb 3, 2021 at 5:54 PM Michael Catanzaro <mcatanzaro@xxxxxxxxx> wrote:
>>
>> Hi,
>>
>> Has anybody investigated Jim Salter's claims that Fedora 32 is slow to
>> launch applications? Recent article:
>>
>> https://arstechnica.com/gadgets/2021/02/ubuntu-core-20-adds-secure-boot-with-hardware-backed-encryption/
>>
>> "in my experience, Fedora 32 is noticeably, demonstrably more sluggish
>> to launch applications than Ubuntu is in general."
>>
>> Original article:
>>
>> https://arstechnica.com/gadgets/2020/05/linux-distro-review-fedora-workstation-32/
>>
>> Would be good to know, for starters, whether this difference is real
>> and measurable.
>
> This was bugging me for a while. I also noticed that Fedora 32 is a bit slower than it used to be. Compilation time of a project that I'm working on went from ~35-36 seconds to ~47-48. At first I thought that it's just another round of CPU vulnerabilities mitigations that introduced a performance drop. But after some digging I found that the default CPU governor was switched from 'ondemand' to 'schedutil' in Fedora kernel 5.9.7:
> https://src.fedoraproject.org/rpms/kernel/c/73c86ebaee23df8310b903c1dab2176d443f5a3a?branch=rawhide
> (see configs/fedora/generic/CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL)
>
> I switched it back using cpupower from kernel-tools:
> $ sudo cpupower frequency-set --governor ondemand
>
> And confirmed that my compilation time went back to the previous ~35 seconds.
> In the end I switched the governor to 'performance' and shaved another 5 seconds. And gnome-shell no longer feels sluggish, switching tabs in the browser is also instant.
> To make the change permanent I used settings in /etc/sysconfig/cpupower and enabled cpupower service:
> $ sudo systemctl enable --now cpupower.service
>
> The change of the default CPU governor looks pretty significant to me, but I couldn't find any discussions about it.

CCing the Fedora kernel list and Justin. At the ARK tree level, the
change was introduced in this commit, with no explanation:
https://gitlab.com/cki-project/kernel-ark/commit/9d69ad49ab90db607e25a99eacbf31dc9e513dfa

Justin, do you remember the reason for the change? Can/should it be reverted?

--
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.
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