[Xen-devel] epoll_wait() exceeds timeout

[Pavlo Suikov <pavlo.suikov@xxxxxxxxxxxxxxx>]

Hi,

our setup looks like this:

Hardware: ARMv7, TI Jacinto6

Xen: 4.4-rc1

dom0: Linux 3.8.13

domU: Android 4.3 with Linux kernel 3.8.13

Network: ethernet over USB. USB is mapped 1 to 1 to domU. Use-case: reading from the network socket using epoll_wait() with timeout being set to less than 4 ms (it varies from call to call, but is always less than 4 ms as required by the algorithm). What we observe is: on a bare metal setup timeouts are always met:

1) Android4.3 - without Xen

epoll_wait 3 ms: timeout = 3 ms

epoll_wait 2 ms: timeout = 2 ms

epoll_wait 3 ms: timeout = 3 ms

epoll_wait 2 ms: timeout = 2 ms

epoll_wait 3 ms: timeout = 3 ms

On the same system as a domU in Xen timeouts are exceeded by of 4 to 8 ms:

1) Android4.3 - Xen

epoll_wait 9 ms: timeout = 1 ms

epoll_wait 8 ms: timeout = 1 ms

epoll_wait 7 ms: timeout = 3 ms

epoll_wait 8 ms: timeout = 1 ms

epoll_wait 7 ms: timeout = 3 ms

epoll_wait() returns with a correct return value (timeout), but it blocks the thread for much longer time than it should.

As we had already issues with the scheduler, we have made tests with pCPU pinned to vCPUs, so no Xen scheduling should interfere with the timings (and the cyclictest is doing well): timeouts are still exceeded.

Has anyone faced the same problem or has suggestion on what can possibly be causing it?

Suikov Pavlo
GlobalLogic
M +38.066.667.1296  S psujkov
www.globallogic.com

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