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To:     Marcelo Tosatti <mtosatti@redhat.com>,
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Cc:     Borislav Petkov <bp@alien8.de>, Minchan Kim <minchan@kernel.org>,
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        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