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Subject5.5-rc1 regression with BNXT firmware driver
Date
Hi,

I've been hunting down some hackbench regression between 5.4-rc8 and 5.5-rc1
on my Juno r0, one of the offenders seems to be:

246880958ac9 ("firmware: broadcom: add OP-TEE based BNXT f/w manager")

This is tested on a kernel built with defconfig (TEE_BNXT_FW gets selected)
and with:

echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo performance > /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor
./perf stat --null --sync --repeat 200 ./hackbench

The regression is easily reproducible on my end, this is 3 runs of the above
comparing the patch and its parent:

-PATCH:
0.71062 +- 0.00150 seconds time elapsed ( +- 0.21% )
0.71121 +- 0.00181 seconds time elapsed ( +- 0.25% )
0.71277 +- 0.00181 seconds time elapsed ( +- 0.25% )

+PATCH:
0.72556 +- 0.00174 seconds time elapsed ( +- 0.24% )
0.72695 +- 0.00192 seconds time elapsed ( +- 0.26% )
0.72559 +- 0.00178 seconds time elapsed ( +- 0.25% )


AIUI Vincent found something different while hunting down a similar
regression:

df323337e507 ("apparmor: Use a memory pool instead per-CPU caches")

but it seems this one is another cause. Seeing as this involves security
stuff the overhead may be acceptable, nevertheless now that I have some
reproducer I figured I'd send this out.

Cheers,
Valentin

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