[Xen-devel] Delays on usleep calls

[Pavlo Suikov <pavlo.suikov@xxxxxxxxxxxxxxx>]

Hi,

yet another question on soft real time under Xen. Setup looks like this:

Xen: 4.4-rc1 with credit scheduler

dom0: Linux 3.8.13 with CFS scheduler

domU: Android 4.3 with Linux kernel 3.8.13 with CFS scheduler

Test program makes nothing but sleeping for 30 (5, 500) ms then printing timestamp in an endless loop. Results on a guest OS being run without hypervisor are pretty correct, while on a guest OS under a hypervisor (both in dom0 and domU) we observe regular delay of 5-15 ms no matter what sleep time is. Configuring scheduler to different weights for dom0/domU has no effect whatsoever.

If setup looks like this (the only change is the Xen scheduler):

Xen: 4.4-rc1 with sEDF scheduler

dom0: Linux 3.8.13 with CFS scheduler

domU: Android 4.3 with Linux kernel 3.8.13 with CFS scheduler

we observe the same delay but only in domU; dom0 measurements are far more correct.

Can anyone suggest what can be a reason for such a misbehaviour and what can be impacted by it? We came to this test from an incorrect rendering timer work, but it seems that there is an issue on it's own. If anyone can suggest more precise tests, it would be appreciated as well; system activity in the guest OS is the same for tests with and without Xen.

Thanks in advance!

Suikov Pavlo
GlobalLogic
P +x.xxx.xxx.xxxx  M +38.066.667.1296  S psujkov
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