On Thu, 2010-08-12 at 20:57 +0100, Chris Wilson wrote: > 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.
You should rebase this on -rc1 or above since the stuff in the kernel changed and we don't use the slow work stuff anymore. Dave. > > 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 > > Signed-off-by: Chris Wilson <[email protected]> > Reported-and-tested-by: Bruno Prémont <[email protected]> > --- > 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); _______________________________________________ dri-devel mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/dri-devel
