Bug 46578

Summary:	Xorg client scheduling has bad defaults (/algorithm)
Product:	xorg	Reporter:	Lauri Kasanen <cand>
Component:	Server/General	Assignee:	Adam Jackson <ajax>
Status:	RESOLVED FIXED	QA Contact:	Xorg Project Team <xorg-team>
Severity:	normal
Priority:	medium	CC:	ajax
Version:	git
Hardware:	All
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:

Description Lauri Kasanen 2012-02-24 08:59:53 UTC

Adding a bug so this doesn't get lost. For the background see:
http://lists.freedesktop.org/archives/xorg/2012-January/054029.html

In short, the server ignores a client even if it has time to respond to it. This causes delays of up to 30ms to the ignored client, which is stuck in a call such as xquerypointer.

Comment 1 Alan Coopersmith 2013-10-19 04:47:59 UTC

Archives got rebuilt/renumbered so the old link is invalid.
New link seems to be:
http://lists.x.org/archives/xorg/2012-January/053821.html
http://lists.x.org/archives/xorg/2012-January/053826.html

Comment 2 Chris Wilson 2013-10-19 09:09:59 UTC

Also relevant: http://lists.x.org/archives/xorg-devel/2013-October/038135.html

Comment 3 Adam Jackson 2014-03-27 17:42:28 UTC

This is mostly fixed now, by:

commit c1ce807d9f18f215332d7eeb844e8c640f71c53c
Author: Keith Packard <keithp@keithp.com>
Date:   Wed Jan 22 11:01:59 2014 -0800

    dix: Praise clients which haven't run for a while, rather than idle clients

commit b61ccd5d9d368f3fbbae27ce14ac02a3db1884c4
Author: Adam Jackson <ajax@redhat.com>
Date:   Tue Nov 5 10:20:04 2013 -0500

    smartsched: Tweak the default scheduler intervals

We will now select() afresh every time we switch clients, and rely on the scheduler scores to pick the most-deserving client each time through.  It's _possible_ that we should instead try to drain every ready fd every time we call select(), but I'm not totally convinced, and it would require a lot of algorithmic changes to our main loop to maintain both fairness and responsiveness.  If we were a webserver it might make sense to maximize throughput like that, but probably we should consider select() cheap enough that we can just rely on the scheduler scores.

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