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Date:   Sun, 22 May 2022 01:22:00 +0200
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To:     Marcelo Tosatti <mtosatti@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc:     Borislav Petkov <bp@alien8.de>, Minchan Kim <minchan@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Juri Lelli <juri.lelli@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Phil Elwell <phil@raspberrypi.com>, regressions@lists.linux.dev
From:   Stefan Wahren <stefan.wahren@i2se.com>
Subject: vchiq: Performance regression since 5.18-rc1
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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