From: Daniel Vetter <daniel.vetter@xxxxxxxx> [ Upstream commit 18d0952a838ba559655b0cd9cf85097ad63d9bca ] The issue we have is that the crc worker might fall behind. We've tried to handle this by tracking both the earliest frame for which it still needs to compute a crc, and the last one. Plus when the crtc_state changes, we have a new work item, which are all run in order due to the ordered workqueue we allocate for each vkms crtc. Trouble is there's been a few small issues in the current code: - we need to capture frame_end in the vblank hrtimer, not in the worker. The worker might run much later, and then we generate a lot of crc for which there's already a different worker queued up. - frame number might be 0, so create a new crc_pending boolean to track this without confusion. - we need to atomically grab frame_start/end and clear it, so do that all in one go. This is not going to create a new race, because if we race with the hrtimer then our work will be re-run. - only race that can happen is the following: 1. worker starts 2. hrtimer runs and updates frame_end 3. worker grabs frame_start/end, already reading the new frame_end, and clears crc_pending 4. hrtimer calls queue_work() 5. worker completes 6. worker gets re-run, crc_pending is false Explain this case a bit better by rewording the comment. v2: Demote warning level output to debug when we fail to requeue, this is expected under high load when the crc worker can't quite keep up. Cc: Shayenne Moura <shayenneluzmoura@xxxxxxxxx> Cc: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx> Cc: Haneen Mohammed <hamohammed.sa@xxxxxxxxx> Cc: Daniel Vetter <daniel@xxxxxxxx> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx> Tested-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20190606222751.32567-2-daniel.vetter@xxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/gpu/drm/vkms/vkms_crc.c | 27 +++++++++++++-------------- drivers/gpu/drm/vkms/vkms_crtc.c | 9 +++++++-- drivers/gpu/drm/vkms/vkms_drv.h | 2 ++ 3 files changed, 22 insertions(+), 16 deletions(-) diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c index d7b409a3c0f8c..66603da634fe3 100644 --- a/drivers/gpu/drm/vkms/vkms_crc.c +++ b/drivers/gpu/drm/vkms/vkms_crc.c @@ -166,16 +166,24 @@ void vkms_crc_work_handle(struct work_struct *work) struct drm_plane *plane; u32 crc32 = 0; u64 frame_start, frame_end; + bool crc_pending; unsigned long flags; spin_lock_irqsave(&out->state_lock, flags); frame_start = crtc_state->frame_start; frame_end = crtc_state->frame_end; + crc_pending = crtc_state->crc_pending; + crtc_state->frame_start = 0; + crtc_state->frame_end = 0; + crtc_state->crc_pending = false; spin_unlock_irqrestore(&out->state_lock, flags); - /* _vblank_handle() hasn't updated frame_start yet */ - if (!frame_start || frame_start == frame_end) - goto out; + /* + * We raced with the vblank hrtimer and previous work already computed + * the crc, nothing to do. + */ + if (!crc_pending) + return; drm_for_each_plane(plane, &vdev->drm) { struct vkms_plane_state *vplane_state; @@ -196,20 +204,11 @@ void vkms_crc_work_handle(struct work_struct *work) if (primary_crc) crc32 = _vkms_get_crc(primary_crc, cursor_crc); - frame_end = drm_crtc_accurate_vblank_count(crtc); - - /* queue_work can fail to schedule crc_work; add crc for - * missing frames + /* + * The worker can fall behind the vblank hrtimer, make sure we catch up. */ while (frame_start <= frame_end) drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32); - -out: - /* to avoid using the same value for frame number again */ - spin_lock_irqsave(&out->state_lock, flags); - crtc_state->frame_end = frame_end; - crtc_state->frame_start = 0; - spin_unlock_irqrestore(&out->state_lock, flags); } static int vkms_crc_parse_source(const char *src_name, bool *enabled) diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c index e447b7588d06e..77a1f5fa5d5c8 100644 --- a/drivers/gpu/drm/vkms/vkms_crtc.c +++ b/drivers/gpu/drm/vkms/vkms_crtc.c @@ -30,13 +30,18 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer) * has read the data */ spin_lock(&output->state_lock); - if (!state->frame_start) + if (!state->crc_pending) state->frame_start = frame; + else + DRM_DEBUG_DRIVER("crc worker falling behind, frame_start: %llu, frame_end: %llu\n", + state->frame_start, frame); + state->frame_end = frame; + state->crc_pending = true; spin_unlock(&output->state_lock); ret = queue_work(output->crc_workq, &state->crc_work); if (!ret) - DRM_WARN("failed to queue vkms_crc_work_handle"); + DRM_DEBUG_DRIVER("vkms_crc_work_handle already queued\n"); } spin_unlock(&output->lock); diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h index 81f1cfbeb9362..3c7e06b19efd5 100644 --- a/drivers/gpu/drm/vkms/vkms_drv.h +++ b/drivers/gpu/drm/vkms/vkms_drv.h @@ -56,6 +56,8 @@ struct vkms_plane_state { struct vkms_crtc_state { struct drm_crtc_state base; struct work_struct crc_work; + + bool crc_pending; u64 frame_start; u64 frame_end; }; -- 2.20.1
