drm/i915: Default to a more lenient forced preemption timeout

Based on a sampling of a number of benchmarks across platforms, by
default opt for a much more lenient timeout so that we should not
adversely affect existing "good" clients.

640ms ought to be enough for anyone.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112169
Fixes: 3a7a92ab ("drm/i915/execlists: Force preemption")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Eero Tamminen <eero.t.tamminen@intel.com>
Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191125162737.2161069-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/Kconfig.profile

@@ -25,7 +25,7 @@ config DRM_I915_HEARTBEAT_INTERVAL
 
 config DRM_I915_PREEMPT_TIMEOUT
 	int "Preempt timeout (ms, jiffy granularity)"
-	default 100 # milliseconds
+	default 640 # milliseconds
 	help
 	  How long to wait (in milliseconds) for a preemption event to occur
 	  when submitting a new context via execlists. If the current context