On Wed, Jun 24, 2020 at 01:18:42PM +0200, Kamil Konieczny wrote: > Hi, > > On 24.06.2020 12:32, Lukasz Luba wrote: > > Hi Krzysztof and Willy > > > > On 6/23/20 8:11 PM, Krzysztof Kozlowski wrote: > >> 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://protect2.fireeye.com/url?k=c364e88a-9eb6fe2f-c36563c5-0cc47a31bee8-631885f0a63a11a0&q=1&u=https%3A%2F%2Fgithub.com%2Fwwilly%2Fbenchmark.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. > > > > Thanks Krzysztof for adding me here. > > > >> > >> 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... > > > > I had issues with devfreq governor which wasn't called by devfreq > > workqueue. The old DELAYED vs DEFERRED work discussions and my patches > > for it [1]. If the CPU which scheduled the next work went idle, the > > devfreq workqueue will not be kicked and devfreq governor won't check > > DMC status and will not decide to decrease the frequency based on low > > busy_time. > > The same applies for going up with the frequency. They both are > > done by the governor but the workqueue must be scheduled periodically. > > > > I couldn't do much with this back then. I have given the example that > > this is causing issues with the DMC [2]. There is also a description > > of your situation staying at 633MHz for long time: > > ' When it is missing opportunity > > to change the frequency, it can either harm the performance or power > > consumption, depending of the frequency the device stuck on.' > > > > The patches were not accepted because it will cause CPU wake-up from > > idle, which increases the energy consumption. I know that there were > > some other attempts, but I don't know the status. > > > > I had also this devfreq workqueue issue when I have been working on > > thermal cooling for devfreq. The device status was not updated, because > > the devfreq workqueue didn't check the device [3]. > > > > Let me investigate if that is the case. > > > > Regards, > > Lukasz > > > > [1] https%3A%2F%2Flkml.org%2Flkml%2F2019%2F2%2F11%2F1146 > > [2] https%3A%2F%2Flkml.org%2Flkml%2F2019%2F2%2F12%2F383 > > [3] https%3A%2F%2Flwn.net%2Fml%2Flinux-kernel%2F20200511111912.3001-11-lukasz.luba%40arm.com%2F > > and here was another try to fix wq: "PM / devfreq: add possibility for delayed work" > > https://lkml.org/lkml/2019/12/9/486 My case was clearly showing wrong behavior. System was idle but not sleeping - network working, SSH connection ongoing. Therefore at least one CPU was not idle and could adjust the devfreq/DMC... but this did not happen. The system stayed for like a minute in 633 MHz OPP. Not-waking up idle processors - ok... so why not using power efficient workqueue? It is exactly for this purpose - wake up from time to time on whatever CPU to do the necessary job. Best regards, Krzysztof
