drm: Measure Self Refresh Entry/Exit times to avoid thrashing
Currently the self refresh idle timer is a const set by the crtc. This is fine if the self refresh entry/exit times are well-known for all panels used on that crtc. However panels and workloads can vary quite a bit, and a timeout which works well for one doesn't work well for another. In the extreme, if the timeout is too short we could get in a situation where the self refresh exits are taking so long we queue up a self refresh entry before the exit commit is even finished. This patch changes the idle timeout to a moving average of the entry times + a moving average of exit times + the crtc constant. This patch was tested on rockchip, with a kevin CrOS panel the idle delay averages out to about ~235ms (35 entry + 100 exit + 100 const). On the same board, the bob panel idle delay lands around ~340ms (90 entry + 150 exit + 100 const). WRT the dedicated mutex in self_refresh_data, it would be nice if we could rely on drm_crtc.mutex to protect the average times, but there are a few reasons why a separate lock is a better choice: - We can't rely on drm_crtc.mutex being held if we're doing a nonblocking commit - We can't grab drm_crtc.mutex since drm_modeset_lock() doesn't tell us whether the lock was already held in the acquire context (it eats -EALREADY), so we can't tell if we should drop it or not - We don't need such a heavy-handed lock for what we're trying to do, commit ordering doesn't matter, so a point-of-use lock will be less contentious Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Sean Paul <seanpaul@chromium.org> Link to v1: https://patchwork.freedesktop.org/patch/msgid/20190917200443.64481-2-sean@poorly.run Link: https://patchwork.freedesktop.org/patch/msgid/20190918200734.149876-2-sean@poorly.run Changes in v2: - Migrate locking explanation from comment to commit msg (Daniel) - Turf constant entry delay and multiply the avg times by 2 (Daniel)
This commit is contained in:
Sean Paul
parent
2d2e0b90a0
commit
d4da4e3334
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@ -26,6 +26,7 @@
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*/
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#include <linux/dma-fence.h>
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#include <linux/ktime.h>
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#include <drm/drm_atomic.h>
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#include <drm/drm_atomic_helper.h>
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@ -1580,9 +1581,23 @@ static void commit_tail(struct drm_atomic_state *old_state)
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{
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struct drm_device *dev = old_state->dev;
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const struct drm_mode_config_helper_funcs *funcs;
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ktime_t start;
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s64 commit_time_ms;
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funcs = dev->mode_config.helper_private;
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/*
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* We're measuring the _entire_ commit, so the time will vary depending
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* on how many fences and objects are involved. For the purposes of self
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* refresh, this is desirable since it'll give us an idea of how
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* congested things are. This will inform our decision on how often we
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* should enter self refresh after idle.
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*
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* These times will be averaged out in the self refresh helpers to avoid
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* overreacting over one outlier frame
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*/
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start = ktime_get();
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drm_atomic_helper_wait_for_fences(dev, old_state, false);
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drm_atomic_helper_wait_for_dependencies(old_state);
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@ -1592,6 +1607,11 @@ static void commit_tail(struct drm_atomic_state *old_state)
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else
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drm_atomic_helper_commit_tail(old_state);
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commit_time_ms = ktime_ms_delta(ktime_get(), start);
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if (commit_time_ms > 0)
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drm_self_refresh_helper_update_avg_times(old_state,
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(unsigned long)commit_time_ms);
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drm_atomic_helper_commit_cleanup_done(old_state);
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drm_atomic_state_put(old_state);
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@ -5,6 +5,7 @@
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* Authors:
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* Sean Paul <seanpaul@chromium.org>
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*/
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#include <linux/average.h>
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#include <linux/bitops.h>
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#include <linux/slab.h>
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#include <linux/workqueue.h>
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@ -50,10 +51,17 @@
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* atomic_check when &drm_crtc_state.self_refresh_active is true.
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*/
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#define SELF_REFRESH_AVG_SEED_MS 200
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DECLARE_EWMA(psr_time, 4, 4)
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struct drm_self_refresh_data {
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struct drm_crtc *crtc;
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struct delayed_work entry_work;
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unsigned int entry_delay_ms;
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struct mutex avg_mutex;
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struct ewma_psr_time entry_avg_ms;
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struct ewma_psr_time exit_avg_ms;
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};
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static void drm_self_refresh_helper_entry_work(struct work_struct *work)
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@ -121,6 +129,44 @@ static void drm_self_refresh_helper_entry_work(struct work_struct *work)
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drm_modeset_acquire_fini(&ctx);
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}
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/**
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* drm_self_refresh_helper_update_avg_times - Updates a crtc's SR time averages
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* @state: the state which has just been applied to hardware
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* @commit_time_ms: the amount of time in ms that this commit took to complete
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*
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* Called after &drm_mode_config_funcs.atomic_commit_tail, this function will
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* update the average entry/exit self refresh times on self refresh transitions.
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* These averages will be used when calculating how long to delay before
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* entering self refresh mode after activity.
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*/
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void drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
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unsigned int commit_time_ms)
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{
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struct drm_crtc *crtc;
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struct drm_crtc_state *old_crtc_state, *new_crtc_state;
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int i;
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for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state,
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new_crtc_state, i) {
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struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
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struct ewma_psr_time *time;
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if (old_crtc_state->self_refresh_active ==
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new_crtc_state->self_refresh_active)
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continue;
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if (new_crtc_state->self_refresh_active)
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time = &sr_data->entry_avg_ms;
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else
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time = &sr_data->exit_avg_ms;
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mutex_lock(&sr_data->avg_mutex);
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ewma_psr_time_add(time, commit_time_ms);
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mutex_unlock(&sr_data->avg_mutex);
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}
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}
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EXPORT_SYMBOL(drm_self_refresh_helper_update_avg_times);
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/**
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* drm_self_refresh_helper_alter_state - Alters the atomic state for SR exit
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* @state: the state currently being checked
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@ -152,6 +198,7 @@ void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
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for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
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struct drm_self_refresh_data *sr_data;
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unsigned int delay;
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/* Don't trigger the entry timer when we're already in SR */
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if (crtc_state->self_refresh_active)
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@ -161,8 +208,13 @@ void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
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if (!sr_data)
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continue;
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mutex_lock(&sr_data->avg_mutex);
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delay = (ewma_psr_time_read(&sr_data->entry_avg_ms) +
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ewma_psr_time_read(&sr_data->exit_avg_ms)) * 2;
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mutex_unlock(&sr_data->avg_mutex);
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mod_delayed_work(system_wq, &sr_data->entry_work,
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msecs_to_jiffies(sr_data->entry_delay_ms));
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msecs_to_jiffies(delay));
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}
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}
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EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
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@ -170,12 +222,10 @@ EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
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/**
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* drm_self_refresh_helper_init - Initializes self refresh helpers for a crtc
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* @crtc: the crtc which supports self refresh supported displays
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* @entry_delay_ms: amount of inactivity to wait before entering self refresh
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*
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* Returns zero if successful or -errno on failure
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*/
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int drm_self_refresh_helper_init(struct drm_crtc *crtc,
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unsigned int entry_delay_ms)
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int drm_self_refresh_helper_init(struct drm_crtc *crtc)
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{
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struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
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@ -189,8 +239,18 @@ int drm_self_refresh_helper_init(struct drm_crtc *crtc,
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INIT_DELAYED_WORK(&sr_data->entry_work,
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drm_self_refresh_helper_entry_work);
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sr_data->entry_delay_ms = entry_delay_ms;
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sr_data->crtc = crtc;
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mutex_init(&sr_data->avg_mutex);
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ewma_psr_time_init(&sr_data->entry_avg_ms);
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ewma_psr_time_init(&sr_data->exit_avg_ms);
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/*
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* Seed the averages so they're non-zero (and sufficiently large
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* for even poorly performing panels). As time goes on, this will be
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* averaged out and the values will trend to their true value.
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*/
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ewma_psr_time_add(&sr_data->entry_avg_ms, SELF_REFRESH_AVG_SEED_MS);
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ewma_psr_time_add(&sr_data->exit_avg_ms, SELF_REFRESH_AVG_SEED_MS);
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crtc->self_refresh_data = sr_data;
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return 0;
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@ -39,8 +39,6 @@
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#include "rockchip_drm_vop.h"
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#include "rockchip_rgb.h"
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#define VOP_SELF_REFRESH_ENTRY_DELAY_MS 100
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#define VOP_WIN_SET(vop, win, name, v) \
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vop_reg_set(vop, &win->phy->name, win->base, ~0, v, #name)
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#define VOP_SCL_SET(vop, win, name, v) \
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@ -1563,8 +1561,7 @@ static int vop_create_crtc(struct vop *vop)
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init_completion(&vop->line_flag_completion);
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crtc->port = port;
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ret = drm_self_refresh_helper_init(crtc,
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VOP_SELF_REFRESH_ENTRY_DELAY_MS);
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ret = drm_self_refresh_helper_init(crtc);
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if (ret)
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DRM_DEV_DEBUG_KMS(vop->dev,
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"Failed to init %s with SR helpers %d, ignoring\n",
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@ -12,9 +12,9 @@ struct drm_atomic_state;
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struct drm_crtc;
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void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state);
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void drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
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unsigned int commit_time_ms);
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int drm_self_refresh_helper_init(struct drm_crtc *crtc,
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unsigned int entry_delay_ms);
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int drm_self_refresh_helper_init(struct drm_crtc *crtc);
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void drm_self_refresh_helper_cleanup(struct drm_crtc *crtc);
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#endif
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