Re: platform/x86/intel/pmc: regression found in commit 804951203aa541ad6720c9726c173d18aeb3ab6b

[Linux regression tracking #adding (Thorsten Leemhuis)]

[TLDR: I'm adding this report to the list of tracked Linux kernel
regressions; the text you find below is based on a few templates
paragraphs you might have encountered already in similar form.
See link in footer if these mails annoy you.]

On 13.11.23 16:42, James Hutchinson wrote:
> Running here on an Intel NUC 8i3BEH Coffee Lake machine under Arch Linux.
> 
> Connected to this machine I have 4x USB DVB Cards (2xDVBSky S960
> DVB-S2 adapters & 2xGeniatech T230 DVB-T2 adapters), and I stream TV
> Channels around the house via Tvheadend.
> 
> Since linux kernel v6.5 onwards I noticed a bad performance regression
> whereby the streams are basically unstable. There are tons of
> continuity errors in the Tvheadend logfile, and the picture and sound
> are badly broken up as though the system is throttled or does not have
> the bandwidth to cope with the streams.
> 
> Sometimes the stream will work for a minute or so after reboot, before
> then becoming unstable, and then seems to remain unstable until the
> next cold reboot.
> 
> I dropped back to v6.1 LTS (where everything is fine) and re-tested
> following the release of v6.6...
> ...the problem had not gone away so I performed a git bisect to
> identify the culprit and found this to be:
> 
> 804951203aa541ad6720c9726c173d18aeb3ab6b: platform/x86:intel/pmc:
> Combine core_init() and core_configure()
> 
> I can work around the issue by either reverting this commit or by
> disabling CONFIG_INTEL_PMC_CORE and rebuilding the kernel manually,
> either of which results in perfect DVB streaming once more.
> 
> Happy to test any potential patches or otherwise provide further
> information as required.

Thanks for the report. To be sure the issue doesn't fall through the
cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression
tracking bot:

#regzbot ^introduced 804951203aa541ad6720c9726
https://bugzilla.kernel.org/show_bug.cgi?id=218143
#regzbot title platform/x86/intel/pmc: bad performance regression
whereby the TV streams are basically unstable
#regzbot ignore-activity

This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply and tell me -- ideally
while also telling regzbot about it, as explained by the page listed in
the footer of this mail.

Developers: When fixing the issue, remember to add 'Link:' tags pointing
to the report (the parent of this mail). See page linked in footer for
details.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
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