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Polling for a VGA device on an old system can be quite expensive, causing latencies on the order of 600ms. As we hold the mode mutex for this time and also need the same mutex to move the cursor, we trigger a user-visible stall. The real solution would involve improving the granulatity of the locking and so perhaps performing some of the probing not under the lock or some other updates can be done under different locks. Also reducing the cost of probing for a non-existent monitor would be worthwhile. However, exposing a parameter to disable polling is a simple workaround in the meantime. In order to accommodate users turning polling on and off at runtime, the polling is potentially re-enabled on every probe. This is coupled to the user calling xrandr, which seems to be a vaild time to reset the polling timeout since the information on the connection has just been updated. (The presumption being that all connections are probed in a single xrandr pass, which is currently valid.) References: Bug 29536 - 2.6.35 causes ~600ms latency every 10s https://bugs.freedesktop.org/show_bug.cgi?id=29536 Bug 16265 - Why is kslowd accumulating so much CPU time? https://bugzilla.kernel.org/show_bug.cgi?id=16265 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reported-and-tested-by: Bruno Prémont <bonbons@linux-vserver.org> Signed-off-by: Dave Airlie <airlied@redhat.com>
************************************************************ * For the very latest on DRI development, please see: * * http://dri.freedesktop.org/ * ************************************************************ The Direct Rendering Manager (drm) is a device-independent kernel-level device driver that provides support for the XFree86 Direct Rendering Infrastructure (DRI). The DRM supports the Direct Rendering Infrastructure (DRI) in four major ways: 1. The DRM provides synchronized access to the graphics hardware via the use of an optimized two-tiered lock. 2. The DRM enforces the DRI security policy for access to the graphics hardware by only allowing authenticated X11 clients access to restricted regions of memory. 3. The DRM provides a generic DMA engine, complete with multiple queues and the ability to detect the need for an OpenGL context switch. 4. The DRM is extensible via the use of small device-specific modules that rely extensively on the API exported by the DRM module. Documentation on the DRI is available from: http://dri.freedesktop.org/wiki/Documentation http://sourceforge.net/project/showfiles.php?group_id=387 http://dri.sourceforge.net/doc/ For specific information about kernel-level support, see: The Direct Rendering Manager, Kernel Support for the Direct Rendering Infrastructure http://dri.sourceforge.net/doc/drm_low_level.html Hardware Locking for the Direct Rendering Infrastructure http://dri.sourceforge.net/doc/hardware_locking_low_level.html A Security Analysis of the Direct Rendering Infrastructure http://dri.sourceforge.net/doc/security_low_level.html