[Bug 109830] CPU iowait higher when run the GPU multi decoding threads

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109830

--- Comment #37 from Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com> ---
Ignoring these patches for now, but with pre-caching and output to /dev/null
only. The iowait is still the same? I am still curious about that device mapper
patch - since you said the i915 patch on it's own is not enough to bring the
iowait down.

Otherwise, a single test job from your scripts spends ~12% of it's runtime in
GEM_WAIT ioctl - which is the source of iowait.

When you run 34 this jobs in parallel the waits will naturally scale up due GPU
being more congested.

In other words userspace seems to be deliberately waiting on the GPU and if you
want to decrease reported iowait you could also try making userspace more
asynchronous.

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