Subject: Re: performance drop with alpine linux upgrade
To: alice <alice@ayaya.dev>, alpine-user <alpine-user@lists.alpinelinux.org>
References: <196e1b55-ade9-8a4b-889b-006fef7f63c1@libero.it>
 <CMUCC7OZ4Y9K.10UWLB8RC8NP8@sumire>
From: Riccardo Mottola <riccardo.mottola@libero.it>
Message-ID: <9cb23b83-bf70-dd44-6249-a69e30e6f3e0@libero.it>
Date: Mon, 12 Sep 2022 14:59:20 +0200
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Hello Alice,


alice wrote:
> On Mon Sep 12, 2022 at 10:47 AM CEST, Riccardo Mottola wrote:
> you should monitor the frequency during that- it probably goes down/up
> as the fans do

cpuinfo gives always the same frequency
>> I can think of two causes, from my past experience with other systems:
>> - disabled caches
> i don't think a kernel update would change this, either
>> - CPU not runnig at full speed
>>
>> In the BIOS I checked and CPU and L2 caches are enabled (small in this
>> crippled CPU anyway).
>> Could some APM/ACPI lower the cpu speed until I rise it withsome governor?
> you can check the governors with:
> cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

my cpu9 does not have cpufreq, either it is not supported at all on this
old CPU model or something is not detected?
That would make me guess however that it runs at the speed shown in
cpuinfo, 2.2GHz.

also:

cervino:~# cpufreq-info
cpufrequtils 008: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq@vger.kernel.org, please.
analyzing CPU 0:

>
> but i don't think even being stuck on "powersave" or something would do
> that.. strange

No, I would, at the opposite, suppose it would be stuck to the frequency
reported in cpuinfo, that is, the maximum

>
> this sounds like some weird kernel regression in 5.15, if anything

strange indeed

5.15.64-0-lts #1-Alpine SMP Mon, 05 Sep 2022 08:02:49 +0000 i686 Linux


in dmesg I see:
[    1.605776] intel_pstate: CPU model not supported


but I don't know if this is relevant, this CPU is based on netburst
architecture. I think that back then, few cpu scaling methods where
available. Original speedstep and perhaps p4_clockmod - where the clock
doesn't really change?

I cannot identify this CPU here:
https://en.wikipedia.org/wiki/List_of_Intel_Celeron_processors#Netburst_based_Celerons

since 2.2Ghz appears to have 128K cache. It could be this one:
https://ark.intel.com/content/www/us/en/ark/products/27318/mobile-intel-celeron-processor-2-20-ghz-256k-cache-400-mhz-fsb.html

still i don't think too much relevant to have the exact detail.


> add mitigations=off to the kernel cmdline, via whatever booting setup
> you have. usual warnings/caveats apply, but there you go. i doubt they
> would be that impactful though..

I doubt too, on more modern CPUs I have found an impact of 1% to 10%
usually... but maybe on this old cache-limited CPU?

I have syslinux, I don't know hot do add that option to
|/etc/update-extlinux.conf|, but I will add it manually for a boot and
test the difference.

Riccardo