On Tue, Jun 23, 2020 at 09:02:38PM +0200, Krzysztof Kozlowski wrote: > On Tue, 23 Jun 2020 at 18:47, Willy Wolff <willy.mh.wolff.ml@xxxxxxxxx> wrote: > > > > Hi everybody, > > > > Is DVFS for memory bus really working on Odroid XU3/4 board? > > Using a simple microbenchmark that is doing only memory accesses, memory DVFS > > seems to not working properly: > > > > The microbenchmark is doing pointer chasing by following index in an array. > > Indices in the array are set to follow a random pattern (cutting prefetcher), > > and forcing RAM access. > > > > git clone https://github.com/wwilly/benchmark.git \ > > && cd benchmark \ > > && source env.sh \ > > && ./bench_build.sh \ > > && bash source/scripts/test_dvfs_mem.sh > > > > Python 3, cmake and sudo rights are required. > > > > Results: > > DVFS CPU with performance governor > > mem_gov = simple_ondemand at 165000000 Hz in idle, should be bumped when the > > benchmark is running. > > - on the LITTLE cluster it takes 4.74308 s to run (683.004 c per memory access), > > - on the big cluster it takes 4.76556 s to run (980.343 c per moemory access). > > > > While forcing DVFS memory bus to use performance governor, > > mem_gov = performance at 825000000 Hz in idle, > > - on the LITTLE cluster it takes 1.1451 s to run (164.894 c per memory access), > > - on the big cluster it takes 1.18448 s to run (243.664 c per memory access). > > > > The kernel used is the last 5.7.5 stable with default exynos_defconfig. > > Thanks for the report. Few thoughts: > 1. What trans_stat are saying? Except DMC driver you can also check > all other devfreq devices (e.g. wcore) - maybe the devfreq events > (nocp) are not properly assigned? > 2. Try running the measurement for ~1 minutes or longer. The counters > might have some delay (which would require probably fixing but the > point is to narrow the problem). > 3. What do you understand by "mem_gov"? Which device is it? +Cc Lukasz who was working on this. I just run memtester and more-or-less ondemand works (at least ramps up): Before: /sys/class/devfreq/10c20000.memory-controller$ cat trans_stat From : To : 165000000 206000000 275000000 413000000 543000000 633000000 728000000 825000000 time(ms) * 165000000: 0 0 0 0 0 0 0 0 1795950 206000000: 1 0 0 0 0 0 0 0 4770 275000000: 0 1 0 0 0 0 0 0 15540 413000000: 0 0 1 0 0 0 0 0 20780 543000000: 0 0 0 1 0 0 0 1 10760 633000000: 0 0 0 0 2 0 0 0 10310 728000000: 0 0 0 0 0 0 0 0 0 825000000: 0 0 0 0 0 2 0 0 25920 Total transition : 9 $ sudo memtester 1G During memtester: /sys/class/devfreq/10c20000.memory-controller$ cat trans_stat From : To : 165000000 206000000 275000000 413000000 543000000 633000000 728000000 825000000 time(ms) 165000000: 0 0 0 0 0 0 0 1 1801490 206000000: 1 0 0 0 0 0 0 0 4770 275000000: 0 1 0 0 0 0 0 0 15540 413000000: 0 0 1 0 0 0 0 0 20780 543000000: 0 0 0 1 0 0 0 2 11090 633000000: 0 0 0 0 3 0 0 0 17210 728000000: 0 0 0 0 0 0 0 0 0 * 825000000: 0 0 0 0 0 3 0 0 169020 Total transition : 13 However after killing memtester it stays at 633 MHz for very long time and does not slow down. This is indeed weird... Best regards, Krzysztof
