Bug 7139 - optimised fbBlt isn't used in Xvnc
Summary: optimised fbBlt isn't used in Xvnc
Alias: None
Product: ThinLinc
Classification: Unclassified
Component: VNC (show other bugs)
Version: 1.3.1
Hardware: PC Unknown
: P2 Normal
Target Milestone: 4.10.0
Assignee: Pierre Ossman
Keywords: prosaic, upstream
Depends on: 5241
Blocks: performance
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Reported: 2018-03-23 15:42 CET by Pierre Ossman
Modified: 2018-09-18 16:17 CEST (History)
1 user (show)

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Description Pierre Ossman cendio 2018-03-23 15:42:46 CET
There is a bug in our version of Xorg that makes fbBlt use an un-optimised code path. This is a fairly common operation so it is important for many use cases that it performs well.

This is fixed in newer versions of Xorg:


A quick test here with glxgears, firefox and some youtube resulted in a decrease of 17% to 12% for fbBlt in its overall CPU usage, as measured by perf.
Comment 1 Pierre Ossman cendio 2018-09-18 16:16:44 CEST
Did a test with Xvnc from 4.9.0 and from build 5901. Manually started Xvnc, no client and just glxgears. perf then reports 34% vs 17% of the time spent in fbBlt.

I can also see the new version calling a sse2 optimised sub-function.

Lastly, glxgears reports a bit higher frame rate (2000 vs 1700).

Seems like we are indeed getting the faster version now.

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