> On 05/28/2015 08:54 PM, Michel Dänzer wrote: >> On 28.05.2015 22:21, Yogi A. Patel wrote: >> Setup - I am using a custom-compiled Linux kernel 3.14.17 on Ubuntu >> 14.04. The kernel is patched with Xenomai using Ipipe >> 3.14.17-x84-4.patch. I have a Radeon HD 8570HD R7 240 graphics card in >> this system. >> >> I can confirm that the radeon driver is compiled and loaded, and by >> running “sudo lshw -C Display”, I can verify that my graphics card is >> using the Radeon driver. >> >> Problem - Now, when I run the latency test in Xenomai, I obtain large >> latencies - up to 40us. If I blacklist the radeon, drm, drm_kms_help, >> ttm, i2c_algo_bit kernel modules, and run the latency test with gdm not >> running, the latencies are under 10us. >> >> In previous kernel versions, such as 3.8.13, I have never seen such big >> differences in latency results between gdm running/not running. > Can you narrow down when the problem was introduced in the kernel, > ideally with git bisect? > > Assuming DPM is enabled, have you tried disabling that with radeon.dpm=0 > on the kernel command line? > > Please attach the dmesg output pertaining to drm/radeon. I did a few experiments and here is an update:
+ It seems that whatever is causing this is from drm/radeon and it came in sometime between 3.8.13 and 3.10.32. The dmesg output from 3.10.32 is attached, too + tests run with Radeon.dpm=0 still show the same issues. + the issue is not due to the model of the card. I swapped out my 8470 and tried a 70xx card and see the same latency issues. + the latencies are worse on 3.14 (40us) than on 3.10 (20-30us) regardless of the card. + latencies on 3.8 for both cards are below 10us. At this moment, I'm not sure I see exactly what is causing the issue or what else to try.
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