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 2019-09-18 16:07:29 -04:00
parent 2d2e0b90a0
commit d4da4e3334
4 changed files with 90 additions and 13 deletions

View File

@ -26,6 +26,7 @@
*/
#include <linux/dma-fence.h>
#include <linux/ktime.h>
#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>
@ -1580,9 +1581,23 @@ static void commit_tail(struct drm_atomic_state *old_state)
{
struct drm_device *dev = old_state->dev;
const struct drm_mode_config_helper_funcs *funcs;
ktime_t start;
s64 commit_time_ms;
funcs = dev->mode_config.helper_private;
/*
* We're measuring the _entire_ commit, so the time will vary depending
* on how many fences and objects are involved. For the purposes of self
* refresh, this is desirable since it'll give us an idea of how
* congested things are. This will inform our decision on how often we
* should enter self refresh after idle.
*
* These times will be averaged out in the self refresh helpers to avoid
* overreacting over one outlier frame
*/
start = ktime_get();
drm_atomic_helper_wait_for_fences(dev, old_state, false);
drm_atomic_helper_wait_for_dependencies(old_state);
@ -1592,6 +1607,11 @@ static void commit_tail(struct drm_atomic_state *old_state)
else
drm_atomic_helper_commit_tail(old_state);
commit_time_ms = ktime_ms_delta(ktime_get(), start);
if (commit_time_ms > 0)
drm_self_refresh_helper_update_avg_times(old_state,
(unsigned long)commit_time_ms);
drm_atomic_helper_commit_cleanup_done(old_state);
drm_atomic_state_put(old_state);

View File

@ -5,6 +5,7 @@
* Authors:
* Sean Paul <seanpaul@chromium.org>
*/
#include <linux/average.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
@ -50,10 +51,17 @@
* atomic_check when &drm_crtc_state.self_refresh_active is true.
*/
#define SELF_REFRESH_AVG_SEED_MS 200
DECLARE_EWMA(psr_time, 4, 4)
struct drm_self_refresh_data {
struct drm_crtc *crtc;
struct delayed_work entry_work;
unsigned int entry_delay_ms;
struct mutex avg_mutex;
struct ewma_psr_time entry_avg_ms;
struct ewma_psr_time exit_avg_ms;
};
static void drm_self_refresh_helper_entry_work(struct work_struct *work)
@ -121,6 +129,44 @@ static void drm_self_refresh_helper_entry_work(struct work_struct *work)
drm_modeset_acquire_fini(&ctx);
}
/**
* drm_self_refresh_helper_update_avg_times - Updates a crtc's SR time averages
* @state: the state which has just been applied to hardware
* @commit_time_ms: the amount of time in ms that this commit took to complete
*
* Called after &drm_mode_config_funcs.atomic_commit_tail, this function will
* update the average entry/exit self refresh times on self refresh transitions.
* These averages will be used when calculating how long to delay before
* entering self refresh mode after activity.
*/
void drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
unsigned int commit_time_ms)
{
struct drm_crtc *crtc;
struct drm_crtc_state *old_crtc_state, *new_crtc_state;
int i;
for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state,
new_crtc_state, i) {
struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
struct ewma_psr_time *time;
if (old_crtc_state->self_refresh_active ==
new_crtc_state->self_refresh_active)
continue;
if (new_crtc_state->self_refresh_active)
time = &sr_data->entry_avg_ms;
else
time = &sr_data->exit_avg_ms;
mutex_lock(&sr_data->avg_mutex);
ewma_psr_time_add(time, commit_time_ms);
mutex_unlock(&sr_data->avg_mutex);
}
}
EXPORT_SYMBOL(drm_self_refresh_helper_update_avg_times);
/**
* drm_self_refresh_helper_alter_state - Alters the atomic state for SR exit
* @state: the state currently being checked
@ -152,6 +198,7 @@ void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
struct drm_self_refresh_data *sr_data;
unsigned int delay;
/* Don't trigger the entry timer when we're already in SR */
if (crtc_state->self_refresh_active)
@ -161,8 +208,13 @@ void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
if (!sr_data)
continue;
mutex_lock(&sr_data->avg_mutex);
delay = (ewma_psr_time_read(&sr_data->entry_avg_ms) +
ewma_psr_time_read(&sr_data->exit_avg_ms)) * 2;
mutex_unlock(&sr_data->avg_mutex);
mod_delayed_work(system_wq, &sr_data->entry_work,
msecs_to_jiffies(sr_data->entry_delay_ms));
msecs_to_jiffies(delay));
}
}
EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
@ -170,12 +222,10 @@ EXPORT_SYMBOL(drm_self_refresh_helper_alter_state);
/**
* drm_self_refresh_helper_init - Initializes self refresh helpers for a crtc
* @crtc: the crtc which supports self refresh supported displays
* @entry_delay_ms: amount of inactivity to wait before entering self refresh
*
* Returns zero if successful or -errno on failure
*/
int drm_self_refresh_helper_init(struct drm_crtc *crtc,
unsigned int entry_delay_ms)
int drm_self_refresh_helper_init(struct drm_crtc *crtc)
{
struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
@ -189,8 +239,18 @@ int drm_self_refresh_helper_init(struct drm_crtc *crtc,
INIT_DELAYED_WORK(&sr_data->entry_work,
drm_self_refresh_helper_entry_work);
sr_data->entry_delay_ms = entry_delay_ms;
sr_data->crtc = crtc;
mutex_init(&sr_data->avg_mutex);
ewma_psr_time_init(&sr_data->entry_avg_ms);
ewma_psr_time_init(&sr_data->exit_avg_ms);
/*
* Seed the averages so they're non-zero (and sufficiently large
* for even poorly performing panels). As time goes on, this will be
* averaged out and the values will trend to their true value.
*/
ewma_psr_time_add(&sr_data->entry_avg_ms, SELF_REFRESH_AVG_SEED_MS);
ewma_psr_time_add(&sr_data->exit_avg_ms, SELF_REFRESH_AVG_SEED_MS);
crtc->self_refresh_data = sr_data;
return 0;

View File

@ -39,8 +39,6 @@
#include "rockchip_drm_vop.h"
#include "rockchip_rgb.h"
#define VOP_SELF_REFRESH_ENTRY_DELAY_MS 100
#define VOP_WIN_SET(vop, win, name, v) \
vop_reg_set(vop, &win->phy->name, win->base, ~0, v, #name)
#define VOP_SCL_SET(vop, win, name, v) \
@ -1563,8 +1561,7 @@ static int vop_create_crtc(struct vop *vop)
init_completion(&vop->line_flag_completion);
crtc->port = port;
ret = drm_self_refresh_helper_init(crtc,
VOP_SELF_REFRESH_ENTRY_DELAY_MS);
ret = drm_self_refresh_helper_init(crtc);
if (ret)
DRM_DEV_DEBUG_KMS(vop->dev,
"Failed to init %s with SR helpers %d, ignoring\n",

View File

@ -12,9 +12,9 @@ struct drm_atomic_state;
struct drm_crtc;
void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state);
void drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
unsigned int commit_time_ms);
int drm_self_refresh_helper_init(struct drm_crtc *crtc,
unsigned int entry_delay_ms);
int drm_self_refresh_helper_init(struct drm_crtc *crtc);
void drm_self_refresh_helper_cleanup(struct drm_crtc *crtc);
#endif