Attachment 37823 Details for Bug 29536 – Workaround, disable polling

[patch] Workaround, disable polling

0001-drm-kms-Add-a-module-parameter-to-disable-polling.patch (text/plain), 3.65 KB, created by Chris Wilson on 2010-08-12 12:56:29 UTC

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Creator: Chris Wilson

Created: 2010-08-12 12:56:29 UTC

Size: 3.65 KB

patch

obsolete

>From 2ea7d0e723d4cab91c1a1793c26eae2a380beae7 Mon Sep 17 00:00:00 2001
>From: Chris Wilson <chris@chris-wilson.co.uk>
>Date: Thu, 12 Aug 2010 19:45:45 +0100
>Subject: [PATCH] drm/kms: Add a module parameter to disable polling
>MIME-Version: 1.0
>Content-Type: text/plain; charset=UTF-8
>Content-Transfer-Encoding: 8bit
>
>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 involving improving the granulatity of the
>locking and 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
>
>Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>Reported-and-tested-by: Bruno PrÃ©mont <bonbons@linux-vserver.org>
>---
> drivers/gpu/drm/drm_crtc_helper.c |   17 +++++++++++++++--
> 1 files changed, 15 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
>index a0ab1d1..13ba313 100644
>--- a/drivers/gpu/drm/drm_crtc_helper.c
>+++ b/drivers/gpu/drm/drm_crtc_helper.c
>@@ -34,6 +34,9 @@
> #include "drm_crtc_helper.h"
> #include "drm_fb_helper.h"
> 
>+static bool drm_kms_helper_poll = true;
>+module_param_named(poll, drm_kms_helper_poll, bool, 0600);
>+
> static void drm_mode_validate_flag(struct drm_connector *connector,
> 				   int flags)
> {
>@@ -99,8 +102,10 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
> 			connector->status = connector_status_disconnected;
> 		if (connector->funcs->force)
> 			connector->funcs->force(connector);
>-	} else
>+	} else {
> 		connector->status = connector->funcs->detect(connector);
>+		drm_helper_hpd_irq_event(dev);
>+	}
> 
> 	if (connector->status == connector_status_disconnected) {
> 		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] disconnected\n",
>@@ -982,6 +987,9 @@ static void output_poll_execute(struct work_struct *work)
> 	enum drm_connector_status old_status, status;
> 	bool repoll = false, changed = false;
> 
>+	if (!drm_kms_helper_poll)
>+		return;
>+
> 	mutex_lock(&dev->mode_config.mutex);
> 	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
> 
>@@ -1032,6 +1040,9 @@ void drm_kms_helper_poll_enable(struct drm_device *dev)
> 	bool poll = false;
> 	struct drm_connector *connector;
> 
>+	if (!dev->mode_config.poll_enabled || !drm_kms_helper_poll)
>+		return;
>+
> 	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
> 		if (connector->polled)
> 			poll = true;
>@@ -1061,8 +1072,10 @@ void drm_helper_hpd_irq_event(struct drm_device *dev)
> {
> 	if (!dev->mode_config.poll_enabled)
> 		return;
>+
> 	/* kill timer and schedule immediate execution, this doesn't block */
> 	cancel_delayed_work(&dev->mode_config.output_poll_work);
>-	queue_delayed_work(system_nrt_wq, &dev->mode_config.output_poll_work, 0);
>+	if (drm_kms_helper_poll)
>+		queue_delayed_work(system_nrt_wq, &dev->mode_config.output_poll_work, 0);
> }
> EXPORT_SYMBOL(drm_helper_hpd_irq_event);
>-- 
>1.7.1
>

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Attachments on bug 29536: 37821 | 37822 | 37823 | 38582

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