Hi Stefan,
On 23/05/2022 07:19, Stefan Wahren wrote:
Hi Paul,
Am 23.05.22 um 06:48 schrieb Paul E. McKenney:
On Sun, May 22, 2022 at 05:11:36PM +0200, Stefan Wahren wrote:
Hi Paul,
Am 22.05.22 um 01:46 schrieb 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/
I tried your patch and Rik's patches but in both cases vchiq_test runs 7
minutes instead of ~ 1 second.
That is surprising. Do you boot with rcupdate.rcu_normal=1?
No, not explicit.
That would
nullify my patch, but I would expect that Rik's patch would still provide
increased performance even in that case.
I will retest with a fresh SD card image.
Could you please characterize where the slowdown is occurring?
Unfortunately i don't have a deep insight into driver and vchiq_test tool. Just
a user view.
Do you think an strace would be a good starting point?
@Phil Any advices to analyse this issue?
Sending many small control packets:
vchiq_test -c 1 10000
essentially tests interrupt latency. Using a small number of large bulk transfers:
vchiq_test -b 10000 1
becomes a test of how long it takes to lock down pages. It also tests DMA
transfer speeds, but since the DMA is run by the firmware (which you aren't
changing), I think you can rule that.
You may also find it helpful to include "force_turbo=1" in config.txt for more
predictable results.
By the way, running our 5.18-rc7-based branch on a 3B+ I'm not seeing any
performance problems:
pi@raspberrypi:~$ time vchiq_test -f 1
Functional test - iters:1
======== iteration 1 ========
Testing bulk transfer for alignment.
Testing bulk transfer at PAGE_SIZE.
real 0m0.512s
user 0m0.042s
sys 0m0.165s
Phil
