Large spikes in latencies

Michel Dänzer michel at
Thu May 28 17:54:43 PDT 2015

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.

Earthling Michel Dänzer               |     
Libre software enthusiast             |             Mesa and X developer

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