Red Hat Bugzilla – Bug 442158
xcb severely cripples X11 performance
Last modified: 2014-06-18 05:10:08 EDT
Description of problem:
The xcb component of libX11 cripples x11 performance over network.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. With a remote X11 server: xwd >test; xwud <test
2. Recompile libX11 with "configure --without-xcb" and install
3. Repeat 1.
With xcb performance is about 28 times worse than without.
Real times of 0.808 secs vs 0.028 secs over 1Gb network.
Xcb should not degrade performance so dramatically.
The libX11 rpm needs modification for build without xcb.
With xcb every write (in _XFlush) is followed by a read (_XEventsQueued) which
is the cause of the very poor performance. The read usually returns EAGAIN
because there is nothing to be read, but it is a severe performace hit anyhow.
And why _XEvenetsQueued/read is being called when select/poll has previously
returned indicating only a single file descriptor was ready is anybody's guess.
Was xcb funded by MS?
I suggest that Fedora not include xcb in default distributions until xcb
demonstrates some tangible benefit, and not retrograde performance.
*** Bug 433263 has been marked as a duplicate of this bug. ***
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upstream fix released:
Nagle's algorithm was mistakenly on.
Please test these builds. I am not sure which side you need to upgrade, so upgrade both to be sure.
Before installing your RPM, typing 'ssh -Y localhost' in a terminal and then opening Firefox, produced a browser that was very slow. Right-click menu took 3 seconds to appear.
I can confirm that your libxcb-1.2-4.fc11.x86_64.rpm solves this issue on Fedora 11 64-bit. After installing the RPM the right-click menu appears instantly.
Thanks a bunch!
libxcb-1.1.91-7.fc10 has been submitted as an update for Fedora 10.
libxcb-1.2-4.fc11 has been submitted as an update for Fedora 11.
libxcb-1.1.91-7.fc10 has been pushed to the Fedora 10 stable repository. If problems still persist, please make note of it in this bug report.
libxcb-1.2-4.fc11 has been pushed to the Fedora 11 stable repository. If problems still persist, please make note of it in this bug report.