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

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Message-ID: <77d6d498-7dd9-03eb-60f2-d7e682bb1b20@i2se.com>
Date:   Sun, 22 May 2022 01:22:00 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     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: vchiq: Performance regression since 5.18-rc1

Hi,

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

Best regards

[1] - https://github.com/raspberrypi/userland