linux-kernel - Re: vchiq: Performance regression since 5.18-rc1

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Date:   Mon, 23 May 2022 11:28:08 +0200
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     Stefan Wahren <stefan.wahren@...e.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>, Minchan Kim <minchan@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Phil Elwell <phil@...pberrypi.com>, regressions@...ts.linux.dev
Subject: Re: vchiq: Performance regression since 5.18-rc1

[TLDR: I'm adding this regression report to the list of tracked
regressions; all text from me you find below is based on a few templates
paragraphs you might have encountered already already in similar form.]

Hi, this is your Linux kernel regression tracker.

On 22.05.22 01:22, Stefan Wahren wrote:
> 
> while testing the staging/vc04_services/interface/vchiq_arm driver with
> my Raspberry Pi 3 B+ (multi_v7_defconfig) i noticed a huge performance
> regression since [ff042f4a9b050895a42cae893cc01fa2ca81b95c] mm:
> lru_cache_disable: replace work queue synchronization with synchronize_rcu
> 
> Usually i run "vchiq_test -f 1" to see the driver is still working [1].
> 
> Before commit:
> 
> real    0m1,500s
> user    0m0,068s
> sys    0m0,846s
> 
> After commit:
> 
> real    7m11,449s
> user    0m2,049s
> sys    0m0,023s

Thanks for the report.

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

#regzbot ^introduced ff042f4a9b050895a42cae893cc01fa2ca81b95
#regzbot title mm: chiq_test runs 7 minutes instead of ~ 1 second.
#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 -- ideally with also
telling regzbot about it, as explained here:
https://linux-regtracking.leemhuis.info/tracked-regression/

Reminder for developers: When fixing the issue, add 'Link:' tags
pointing to the report (the mail this one replied to), as the kernel's
documentation call for; above page explains why this is important for
tracked regressions.

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

P.S.: As the Linux kernel's regression tracker I deal with a lot of
reports and sometimes miss something important when writing mails like
this. If that's the case here, don't hesitate to tell me in a public
reply, it's in everyone's interest to set the public record straight.