From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Brezillon Subject: Re: [PATCH 1/5] drm: don't block fb changes for async plane updates Date: Mon, 11 Mar 2019 11:06:16 +0100 Message-ID: <20190311110616.6b474865@collabora.com> References: <20190304144909.6267-1-helen.koike@collabora.com> <20190304144909.6267-2-helen.koike@collabora.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: "Kazlauskas, Nicholas" Cc: Helen Koike , "dri-devel@lists.freedesktop.org" , "Grodzovsky, Andrey" , "daniel.vetter@ffwll.ch" , "linux-kernel@vger.kernel.org" , Tomasz Figa , David Airlie , Sean Paul , "kernel@collabora.com" , "Wentland, Harry" , =?UTF-8?B?U3TDqXBoYW5l?= Marchesin , Eric Anholt List-Id: dri-devel@lists.freedesktop.org Hello Nicholas, On Mon, 4 Mar 2019 15:46:49 +0000 "Kazlauskas, Nicholas" wrote: > On 3/4/19 9:49 AM, Helen Koike wrote: > > In the case of a normal sync update, the preparation of framebuffers (be > > it calling drm_atomic_helper_prepare_planes() or doing setups with > > drm_framebuffer_get()) are performed in the new_state and the respective > > cleanups are performed in the old_state. > > > > In the case of async updates, the preparation is also done in the > > new_state but the cleanups are done in the new_state (because updates > > are performed in place, i.e. in the current state). > > > > The current code blocks async udpates when the fb is changed, turning > > async updates into sync updates, slowing down cursor updates and > > introducing regressions in igt tests with errors of type: > > > > "CRITICAL: completed 97 cursor updated in a period of 30 flips, we > > expect to complete approximately 15360 updates, with the threshold set > > at 7680" > > > > Fb changes in async updates were prevented to avoid the following scenario: > > > > - Async update, oldfb = NULL, newfb = fb1, prepare fb1, cleanup fb1 > > - Async update, oldfb = fb1, newfb = fb2, prepare fb2, cleanup fb2 > > - Non-async commit, oldfb = fb2, newfb = fb1, prepare fb1, cleanup fb2 (wrong) > > Where we have a single call to prepare fb2 but double cleanup call to fb2. > > > > To solve the above problems, instead of blocking async fb changes, we > > place the old framebuffer in the new_state object, so when the code > > performs cleanups in the new_state it will cleanup the old_fb and we > > will have the following scenario instead: > > > > - Async update, oldfb = NULL, newfb = fb1, prepare fb1, no cleanup > > - Async update, oldfb = fb1, newfb = fb2, prepare fb2, cleanup fb1 > > - Non-async commit, oldfb = fb2, newfb = fb1, prepare fb1, cleanup fb2 > > > > Where calls to prepare/cleanup are ballanced. > > > > Cc: # v4.14+: 25dc194b34dd: drm: Block fb changes for async plane updates > > Fixes: 25dc194b34dd ("drm: Block fb changes for async plane updates") > > Suggested-by: Boris Brezillon > > Signed-off-by: Helen Koike > > > > --- > > Hello, > > > > As mentioned in the cover letter, > > I tested on the rockchip and on i915 (with a patch I am still working on for > > replacing cursors by async update), with igt plane_cursor_legacy and > > kms_cursor_legacy and I didn't see any regressions. > > I couldn't test on MSM and AMD because I don't have the hardware (and I am > > having some issues testing on vc4) and I would appreciate if anyone could help > > me testing those. > > > > I also think it would be a better solution if, instead of having async > > to do in-place updates in the current state, the async path should be > > equivalent to a syncronous update, i.e., modifying new_state and > > performing a flip > > IMHO, the only difference between sync and async should be that async update > > doesn't wait for vblank and applies the changes immeditally to the hw, > > but the code path could be almost the same. > > But for now I think this solution is ok (swaping new_fb/old_fb), and > > then we can adjust things little by little, what do you think? > > > > Thanks! > > Helen > > > > drivers/gpu/drm/drm_atomic_helper.c | 20 ++++++++++---------- > > 1 file changed, 10 insertions(+), 10 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c > > index 540a77a2ade9..e7eb96f1efc2 100644 > > --- a/drivers/gpu/drm/drm_atomic_helper.c > > +++ b/drivers/gpu/drm/drm_atomic_helper.c > > @@ -1608,15 +1608,6 @@ int drm_atomic_helper_async_check(struct drm_device *dev, > > old_plane_state->crtc != new_plane_state->crtc) > > return -EINVAL; > > > > - /* > > - * FIXME: Since prepare_fb and cleanup_fb are always called on > > - * the new_plane_state for async updates we need to block framebuffer > > - * changes. This prevents use of a fb that's been cleaned up and > > - * double cleanups from occuring. > > - */ > > - if (old_plane_state->fb != new_plane_state->fb) > > - return -EINVAL; > > - > > funcs = plane->helper_private; > > if (!funcs->atomic_async_update) > > return -EINVAL; > > @@ -1657,6 +1648,9 @@ void drm_atomic_helper_async_commit(struct drm_device *dev, > > int i; > > > > for_each_new_plane_in_state(state, plane, plane_state, i) { > > + struct drm_framebuffer *new_fb = plane_state->fb; > > + struct drm_framebuffer *old_fb = plane->state->fb; > > + > > funcs = plane->helper_private; > > funcs->atomic_async_update(plane, plane_state); > > > > @@ -1665,11 +1659,17 @@ void drm_atomic_helper_async_commit(struct drm_device *dev, > > * plane->state in-place, make sure at least common > > * properties have been properly updated. > > */ > > - WARN_ON_ONCE(plane->state->fb != plane_state->fb); > > + WARN_ON_ONCE(plane->state->fb != new_fb); > > WARN_ON_ONCE(plane->state->crtc_x != plane_state->crtc_x); > > WARN_ON_ONCE(plane->state->crtc_y != plane_state->crtc_y); > > WARN_ON_ONCE(plane->state->src_x != plane_state->src_x); > > WARN_ON_ONCE(plane->state->src_y != plane_state->src_y); > > + > > + /* > > + * Make sure the FBs have been swapped so that cleanups in the > > + * new_state performs a cleanup in the old FB. > > + */ > > + WARN_ON_ONCE(plane_state->fb != old_fb); > > I personally think this approach is fine and the WARN_ON s are good for > catching drivers that want to use these in the future. Well, I agree this change is the way to go for a short-term solution to relax the old_fb == new_fb constraint, but I keep thinking this whole "update plane_state in place" is a recipe for trouble and just make things more complicated for drivers for no obvious reasons. Look at the VC4 implem [1] if you need a proof that things can get messy pretty quickly. All this state-fields-copying steps could be skipped if the core was simply swapping the old/new states as is done in the sync update path. [1]https://elixir.bootlin.com/linux/v5.0-rc7/source/drivers/gpu/drm/vc4/vc4_plane.c#L878 > > I do think it would be good to add something to the function docs that > explains this requirement and the issue that it addresses. It's a little > unintuitive to require that the old fb is placed into the new state, but > it makes sense as a workaround to this problem. > > Nicholas Kazlauskas > > > } > > } > > EXPORT_SYMBOL(drm_atomic_helper_async_commit); > > >