Re: vchiq: Performance regression since 5.18-rc1

[Paul E. McKenney]

On Sun, May 22, 2022 at 01:22:00AM +0200, Stefan Wahren wrote:
> 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

Please feel free to try the patch shown below.  Or the pair of patches
from Rik here:

https://lore.kernel.org/lkml/20220218183114.2867528-2-riel@xxxxxxxxxxx/
https://lore.kernel.org/lkml/20220218183114.2867528-3-riel@xxxxxxxxxxx/

There is work ongoing to produce something better, but ongoing slowly.
Especially my part of that work.

							Thanx, Paul

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