Messages in this thread | | | Date | Mon, 23 May 2022 10:29:42 +0100 | Subject | Re: vchiq: Performance regression since 5.18-rc1 | From | Phil Elwell <> |
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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@surriel.com/ >>>> https://lore.kernel.org/lkml/20220218183114.2867528-3-riel@surriel.com/ >>> 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
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