Large spikes in latencies

[Yogi A. Patel]

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'll start bisecting, but for now, the dmesg is attached. The dmesg 
output is from the kernel booted with "radeon.dpm=0" and "intremap=off". 
The latter command is because ipipe does not currently support interrupt 
remapping.

Yogi
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[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-3.14.17-xenomai-2.6.4 root=UUID=bf43a50c-721b-49b6-8cef-d6f97aa4daa9 ro quiet splash crashkernel=384M-:128M crashkernel=384M-:128M vt.handoff=7 intremap=off radeon.dpm=0
[    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.14.17-xenomai-2.6.4 root=UUID=bf43a50c-721b-49b6-8cef-d6f97aa4daa9 ro quiet splash crashkernel=384M-:128M crashkernel=384M-:128M vt.handoff=7 intremap=off radeon.dpm=0
[    0.713300] radeon: module has bad taint, not creating trace events
[    0.713832] [drm] radeon kernel modesetting enabled.
[    0.713856] fb: conflicting fb hw usage radeondrmfb vs VESA VGA - removing generic driver
[    0.714432] radeon 0000:01:00.0: VRAM: 1024M 0x0000000000000000 - 0x000000003FFFFFFF (1024M used)
[    0.714433] radeon 0000:01:00.0: GTT: 1024M 0x0000000040000000 - 0x000000007FFFFFFF
[    0.714699] [drm] radeon: 1024M of VRAM memory ready
[    0.714700] [drm] radeon: 1024M of GTT memory ready.
[    0.714800] [drm] radeon/OLAND_mc2.bin: 31452 bytes
[    0.714860] [drm] radeon: power management initialized
[    0.715619] [drm] enabling PCIE gen 3 link speeds, disable with radeon.pcie_gen2=0
[    2.064107] radeon 0000:01:00.0: WB enabled
[    2.064109] radeon 0000:01:00.0: fence driver on ring 0 use gpu addr 0x0000000040000c00 and cpu addr 0xffff88003674ac00
[    2.064110] radeon 0000:01:00.0: fence driver on ring 1 use gpu addr 0x0000000040000c04 and cpu addr 0xffff88003674ac04
[    2.064111] radeon 0000:01:00.0: fence driver on ring 2 use gpu addr 0x0000000040000c08 and cpu addr 0xffff88003674ac08
[    2.064113] radeon 0000:01:00.0: fence driver on ring 3 use gpu addr 0x0000000040000c0c and cpu addr 0xffff88003674ac0c
[    2.064114] radeon 0000:01:00.0: fence driver on ring 4 use gpu addr 0x0000000040000c10 and cpu addr 0xffff88003674ac10
[    2.065655] radeon 0000:01:00.0: fence driver on ring 5 use gpu addr 0x0000000000075a18 and cpu addr 0xffffc900058b5a18
[    2.065673] radeon 0000:01:00.0: irq 47 for MSI/MSI-X
[    2.065681] radeon 0000:01:00.0: radeon: using MSI.
[    2.065706] [drm] radeon: irq initialized.
[    2.699193] fbcon: radeondrmfb (fb0) is primary device
[    2.720286] radeon 0000:01:00.0: fb0: radeondrmfb frame buffer device
[    2.720287] radeon 0000:01:00.0: registered panic notifier
[    2.720294] [drm] Initialized radeon 2.37.0 20080528 for 0000:01:00.0 on minor 0