Aye, you're right, the results of cyclictest are completely different when running as root, here's what I get as a normal user with 4.14.8-rt9-1-rt: [gimmeapill@pill-mobile4 ~]$ cyclictest -S -m -p98 WARN: open /dev/cpu_dma_latency: Permission denied policy: fifo: loadavg: 0.45 0.51 0.23 1/407 1048 T: 0 ( 1044) P:98 I:1000 C: 21816 Min: 2 Act: 9 Avg: 13 Max: 52 T: 1 ( 1045) P:98 I:1500 C: 14541 Min: 3 Act: 24 Avg: 14 Max: 58 T: 2 ( 1046) P:98 I:2000 C: 10903 Min: 3 Act: 15 Avg: 15 Max: 76 T: 3 ( 1047) P:98 I:2500 C: 8721 Min: 3 Act: 4 Avg: 15 Max: 65 and as root: [root@pill-mobile4 gimmeapill]# cyclictest -S -m -p98 # /dev/cpu_dma_latency set to 0us policy: fifo: loadavg: 0.35 0.49 0.22 1/407 1053 T: 0 ( 1050) P:98 I:1000 C: 12415 Min: 2 Act: 4 Avg: 3 Max: 13 T: 1 ( 1051) P:98 I:1500 C: 8272 Min: 2 Act: 4 Avg: 3 Max: 12 T: 2 ( 1052) P:98 I:2000 C: 6201 Min: 3 Act: 4 Avg: 3 Max: 13 T: 3 ( 1053) P:98 I:2500 C: 4958 Min: 3 Act: 4 Avg: 4 Max: 11 My previous tests where meant to compare the performance between RT kernel versions (I just happened to have a root terminal open at that time and didn't think further). For that purpose it worked: I could see a slight degradation since 4.9.x., but yeah, that doesn't help to compare between different systems, better run cyclictest as the audio user. That difference when running as root is nevertheless puzzling, if these results ever translate to real world audio performance, this is really bad. I thought we were done with running audio applications as root for a good 10 years, no? Regarding the CPU difference: it's a notebook processor from 2012 with turbo boost disabled and hyperthreading enabled, set to performance mode. I wouldn't expect it to be fast by today's standards, or to be able to compete core per core with a desktop class cpu of the same era: https://ark.intel.com/products/65707/Intel-Core-i5-3317U-Processor-3M-Cache-... https://ark.intel.com/products/80800/Intel-Celeron-Processor-G1840-2M-Cache-... The single thread performance between those two is also really different, so I wouldn't draw any conclusion regarding latency: https://www.cpubenchmark.net/compare.php?cmp[]=816&cmp[]=2268 BR, LX
PS: What does it all mean? A cheap Intel(R) Celeron(R) CPU G1840 @ 2.80GHz has got less latency, than a much more expensive Intel(R) Core(TM) i5-3317U CPU @ 1.70GHz? How does it affect audio work? What is the relevance of cyclictest? Is the result somehow related to audio latency and/or MIDI jitter?