[Nouveau] [PATCH 1/3] dri2: Implement handling of pageflip completion events.
Mario Kleiner
mario.kleiner at tuebingen.mpg.de
Thu Sep 8 11:06:24 PDT 2011
On Sep 8, 2011, at 12:45 AM, Francisco Jerez wrote:
> Mario Kleiner <mario.kleiner at tuebingen.mpg.de> writes:
>
>> Requests pageflip completion events from the kernel.
>> Implements pageflip completion handler to finalize
>> and timestamp swaps.
>>
>> Completion handler includes a consistency check, and
>> disambiguation if multiple crtc's are involved in a
>> pageflip (e.g., clone mode, extendend desktop). Only
>> the timestamp of the crtc whose vblank event initially
>> triggered the swap is used, but handler waits for flip
>> completion on all involved crtc's before completing the
>> swap and releasing the old framebuffer.
>>
>> This code is almost identical to the code used in the
>> ati/radeon ddx and intel ddx.
>>
> There's a good reason that I held myself back from doing this when I
> wrote the rest of the SwapBuffers stuff; right now the X server
> assumes
> that the DDX can't handle more than one SwapBuffers request in
> flight at
> any given time, so, after a SwapBuffers request has been received, the
> client is prevented from doing anything until the swap (and,
> consequently, the whole rendering of the previous frame) has been
> completed, that means that the client is forced to render each
> frame in
> lock-step, and it leads to a considerable performance loss.
>
> In my judgment it seemed quite dumb to wire up all the page-flipping
> infrastructure together, only to notice that it was slowing things
> down
> even further (since performance was the main point I had for
> it...). As
> the ability to report accurate swap completion events seemed to be of
> comparatively limited usefulness, I made the DDX pretend the
> buffers are
> swapped one frame before they actually are as a temporary workaround
> (see the comment at the end of nouveau_dri2_finish_swap()).
>
Hi, thanks for the comments.
I see your point, but at least as a starting point for the first
iteration i don't think the current dri2 implementation of pageflips
was a dumb decision.
It is the same default "double buffer" behaviour that the binary
drivers on Linux and also on other os'es (OS/X and Windows) expose.
As a default i think it makes sense if an application wants tight
control over presentation timing or - in the case of games - wants to
prevent irritating lag between user input and visual updates -- limit
the number of frames that the game can prerender.
On the intel and ati gpu's, purely double-buffered pageflipping is
already a win for conserving memory bandwidth and because you avoid
blocking the single command fifo for multiple rendering clients, as
you have to if you use vsync'ed copy-blits to avoid tearing. This may
be less of a win on nvidia because they have multiple fifo's or some
independent dma engines if i understand correctly?
Anyway, it's better for performance if clients can queue up multiple
rendered frames for other non-interactive use cases, e.g., benchmarks
or graphics demos. Or if client apps can decide themselves about
presentation timing. That was the point of support for the
oml_sync_control and intel_swap_events extensions and all the
timestamping.
My specific use case for this patchset is a popular free software
toolkit (http://www.psychtoolbox.org) used by neuro-scientists and
brain scientists in general for audio & visual stimulus presentation,
i/o etc. . Nouveau in its current state, at least on the cards i
tested, would be already a very suitable solution for doing this on
linux+nvidia.
The only missing "must-have" feature for such applications are very
reliable and accurate presentation timestamps. Having those puts
nouveau ahead of the binary blob for such apps. The workloads are
usually not as demanding as current games and an occassional skipped
frame is tolerable, but frequently getting wrong/misleading
timestamps of when a frame was presented would be a total show-
stopper. Currently i have to blacklist nouveau in my toolkit just for
that reason.
> So, IMHO, this change depends on the X server N-buffering changes
> going
> in - actually the DRI2SwapLimit() API that (IIRC) Pauli Nieminen
> proposed some time ago was all we needed, but it hasn't been accepted
> upstream for some reason.
>
I was involved in that discussion at the time, iirc. I think having
the DRI2SwapLimit() API would make a lot of sense as a first step and
that those patches just got dropped due to maintainer-overload, not
really too much for technical reasons. To do multi-buffering
correctly, as specified by the oml_sync_control spec, a bit more than
Paul's API for setting the swap_limit would be needed, either on the
ddx driver level or in the x-server itself, e.g., to make sure the
ordering of glXSwapBuffersMscOML() swaps is correct, no more than one
swap gets executed per video refresh and to satisfy the divisor/
remainder constraints correctly if they are used by a client. Special
cases which are not important for typical games or benchmarks but
important for toolkits with precise timing needs. I actually wanted
to work on that, but didn't get around to do it so far. First i'd
like to have nouveau at the same level of timing functionality as ati
and intel.
Could we have an optional nouveau-ddx xorg.conf parameter to select
between the current codepath and the "lower-performance but correct
timestamping" path implemented in these patches? Something like
"EnableTriplebuffering" or "Swaplimit" or
"MaxNumberPrerenderedFrames"? I think having such a setting would
make sense anyway, even if Paul's API is implemented, exactly to
control things like max number of prerendered frames for games and
apps which only use glXSwapBuffers() but should have some control
over input lag.
The latest intel ddx seems to do the same with a "Triplebuffering"
setting.
The setting could default to your current performance implementation.
The path in the new patches would get pretty frequent exercise &
testing by myself and currently a couple of hundred happy neuro-
scientists.
thanks,
-mario
>> Signed-off-by: Mario Kleiner <mario.kleiner at tuebingen.mpg.de>
>> ---
>> src/drmmode_display.c | 105 +++++++++++++++++++++++++++++++++++++
>> ++++++++++--
>> src/nouveau_dri2.c | 89 +++++++++++++++++++++++++++++++++++++
>> ++--
>> src/nv_proto.h | 5 ++-
>> 3 files changed, 189 insertions(+), 10 deletions(-)
>>
>> diff --git a/src/drmmode_display.c b/src/drmmode_display.c
>> index 3afef66..bcb2a94 100644
>> --- a/src/drmmode_display.c
>> +++ b/src/drmmode_display.c
>> @@ -83,6 +83,21 @@ typedef struct {
>> drmmode_prop_ptr props;
>> } drmmode_output_private_rec, *drmmode_output_private_ptr;
>>
>> +typedef struct {
>> + drmmode_ptr drmmode;
>> + unsigned old_fb_id;
>> + int flip_count;
>> + void *event_data;
>> + unsigned int fe_frame;
>> + unsigned int fe_tv_sec;
>> + unsigned int fe_tv_usec;
>> +} drmmode_flipdata_rec, *drmmode_flipdata_ptr;
>> +
>> +typedef struct {
>> + drmmode_flipdata_ptr flipdata;
>> + Bool dispatch_me;
>> +} drmmode_flipevtcarrier_rec, *drmmode_flipevtcarrier_ptr;
>> +
>> static void drmmode_output_dpms(xf86OutputPtr output, int mode);
>>
>> static drmmode_ptr
>> @@ -1246,13 +1261,17 @@ drmmode_cursor_init(ScreenPtr pScreen)
>> }
>>
>> Bool
>> -drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv)
>> +drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
>> + unsigned int ref_crtc_hw_id)
>> {
>> ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>> xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(scrn);
>> drmmode_crtc_private_ptr crtc = config->crtc[0]->driver_private;
>> drmmode_ptr mode = crtc->drmmode;
>> int ret, i, old_fb_id;
>> + int emitted = 0;
>> + drmmode_flipdata_ptr flipdata;
>> + drmmode_flipevtcarrier_ptr flipcarrier;
>>
>> old_fb_id = mode->fb_id;
>> ret = drmModeAddFB(mode->fd, scrn->virtualX, scrn->virtualY,
>> @@ -1265,24 +1284,64 @@ drmmode_page_flip(DrawablePtr draw,
>> PixmapPtr back, void *priv)
>> return FALSE;
>> }
>>
>> + flipdata = calloc(1, sizeof(drmmode_flipdata_rec));
>> + if (!flipdata) {
>> + xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> + "flip queue: data alloc failed.\n");
>> + goto error_undo;
>> + }
>> +
>> + flipdata->event_data = priv;
>> + flipdata->drmmode = mode;
>> +
>> for (i = 0; i < config->num_crtc; i++) {
>> crtc = config->crtc[i]->driver_private;
>>
>> if (!config->crtc[i]->enabled)
>> continue;
>>
>> + flipdata->flip_count++;
>> +
>> + flipcarrier = calloc(1, sizeof(drmmode_flipevtcarrier_rec));
>> + if (!flipcarrier) {
>> + xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> + "flip queue: carrier alloc failed.\n");
>> + if (emitted == 0)
>> + free(flipdata);
>> + goto error_undo;
>> + }
>> +
>> + /* Only the reference crtc will finally deliver its page flip
>> + * completion event. All other crtc's events will be discarded.
>> + */
>> + flipcarrier->dispatch_me = ((1 << i) == ref_crtc_hw_id);
>> + flipcarrier->flipdata = flipdata;
>> +
>> ret = drmModePageFlip(mode->fd, crtc->mode_crtc->crtc_id,
>> - mode->fb_id, 0, priv);
>> + mode->fb_id, DRM_MODE_PAGE_FLIP_EVENT,
>> + flipcarrier);
>> if (ret) {
>> xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> "flip queue failed: %s\n", strerror(errno));
>> - return FALSE;
>> +
>> + free(flipcarrier);
>> + if (emitted == 0)
>> + free(flipdata);
>> + goto error_undo;
>> }
>> +
>> + emitted++;
>> }
>>
>> - drmModeRmFB(mode->fd, old_fb_id);
>> + /* Will release old fb after all crtc's completed flip. */
>> + flipdata->old_fb_id = old_fb_id;
>>
>> return TRUE;
>> +
>> +error_undo:
>> + drmModeRmFB(mode->fd, mode->fb_id);
>> + mode->fb_id = old_fb_id;
>> + return FALSE;
>> }
>>
>> #ifdef HAVE_LIBUDEV
>> @@ -1348,6 +1407,40 @@ drmmode_uevent_fini(ScrnInfoPtr scrn)
>> }
>>
>> static void
>> +drmmode_flip_handler(int fd, unsigned int frame, unsigned int
>> tv_sec,
>> + unsigned int tv_usec, void *event_data)
>> +{
>> + drmmode_flipevtcarrier_ptr flipcarrier = event_data;
>> + drmmode_flipdata_ptr flipdata = flipcarrier->flipdata;
>> + drmmode_ptr drmmode = flipdata->drmmode;
>> +
>> + /* Is this the event whose info shall be delivered to higher
>> level? */
>> + if (flipcarrier->dispatch_me) {
>> + /* Yes: Cache msc, ust for later delivery. */
>> + flipdata->fe_frame = frame;
>> + flipdata->fe_tv_sec = tv_sec;
>> + flipdata->fe_tv_usec = tv_usec;
>> + }
>> + free(flipcarrier);
>> +
>> + /* Last crtc completed flip? */
>> + flipdata->flip_count--;
>> + if (flipdata->flip_count > 0)
>> + return;
>> +
>> + /* Release framebuffer */
>> + drmModeRmFB(drmmode->fd, flipdata->old_fb_id);
>> +
>> + if (flipdata->event_data == NULL)
>> + return;
>> +
>> + /* Deliver cached msc, ust from reference crtc to flip event
>> handler */
>> + nouveau_dri2_flip_event_handler(flipdata->fe_frame, flipdata-
>> >fe_tv_sec,
>> + flipdata->fe_tv_usec, flipdata->event_data);
>> + free(flipdata);
>> +}
>> +
>> +static void
>> drmmode_wakeup_handler(pointer data, int err, pointer p)
>> {
>> ScrnInfoPtr scrn = data;
>> @@ -1377,6 +1470,10 @@ drmmode_screen_init(ScreenPtr pScreen)
>> /* Plug in a vblank event handler */
>> drmmode->event_context.version = DRM_EVENT_CONTEXT_VERSION;
>> drmmode->event_context.vblank_handler =
>> nouveau_dri2_vblank_handler;
>> +
>> + /* Plug in a pageflip completion event handler */
>> + drmmode->event_context.page_flip_handler = drmmode_flip_handler;
>> +
>> AddGeneralSocket(drmmode->fd);
>>
>> /* Register a wakeup handler to get informed on DRM events */
>> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
>> index 1a68ed3..87eaf08 100644
>> --- a/src/nouveau_dri2.c
>> +++ b/src/nouveau_dri2.c
>> @@ -136,6 +136,7 @@ struct nouveau_dri2_vblank_state {
>> DRI2BufferPtr src;
>> DRI2SwapEventPtr func;
>> void *data;
>> + unsigned int frame;
>> };
>>
>> static Bool
>> @@ -222,6 +223,18 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>> unsigned int frame,
>> REGION_INIT(0, ®, (&(BoxRec){ 0, 0, draw->width, draw-
>> >height }), 0);
>> REGION_TRANSLATE(0, ®, draw->x, draw->y);
>>
>> + /* Main crtc for this drawable shall finally deliver pageflip
>> event. */
>> + unsigned int ref_crtc_hw_id = nv_window_belongs_to_crtc(scrn,
>> draw->x,
>> + draw->y,
>> + draw->width,
>> + draw->height);
>> +
>> + /* Whenever first crtc is involved, choose it as reference, as
>> + * its vblank event triggered this swap.
>> + */
>> + if (ref_crtc_hw_id & 1)
>> + ref_crtc_hw_id = 1;
>> +
>> /* Throttle on the previous frame before swapping */
>> nouveau_bo_map(dst_bo, NOUVEAU_BO_RD);
>> nouveau_bo_unmap(dst_bo);
>> @@ -246,7 +259,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>> unsigned int frame,
>>
>> if (DRI2CanFlip(draw)) {
>> type = DRI2_FLIP_COMPLETE;
>> - ret = drmmode_page_flip(draw, src_pix, s);
>> + ret = drmmode_page_flip(draw, src_pix, s, ref_crtc_hw_id);
>> if (!ret)
>> goto out;
>> }
>> @@ -255,6 +268,10 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>> unsigned int frame,
>> SWAP(nouveau_pixmap(dst_pix)->bo, nouveau_pixmap(src_pix)->bo);
>>
>> DamageRegionProcessPending(draw);
>> +
>> + /* If it is a page flip, finish it in the flip event handler. */
>> + if (type == DRI2_FLIP_COMPLETE)
>> + return;
>> } else {
>> type = DRI2_BLIT_COMPLETE;
>>
>> @@ -289,7 +306,7 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>> DrawablePtr draw,
>> DRI2SwapEventPtr func, void *data)
>> {
>> struct nouveau_dri2_vblank_state *s;
>> - CARD64 current_msc;
>> + CARD64 current_msc, expect_msc;
>> int ret;
>>
>> /* Initialize a swap structure */
>> @@ -298,7 +315,7 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>> DrawablePtr draw,
>> return FALSE;
>>
>> *s = (struct nouveau_dri2_vblank_state)
>> - { SWAP, client, draw->id, dst, src, func, data };
>> + { SWAP, client, draw->id, dst, src, func, data, 0 };
>>
>> if (can_sync_to_vblank(draw)) {
>> /* Get current sequence */
>> @@ -316,10 +333,10 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>> DrawablePtr draw,
>> ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
>> DRM_VBLANK_EVENT,
>> max(current_msc, *target_msc - 1),
>> - NULL, NULL, s);
>> + &expect_msc, NULL, s);
>> if (ret)
>> goto fail;
>> -
>> + s->frame = (unsigned int) expect_msc & 0xffffffff;
>> } else {
>> /* We can't/don't want to sync to vblank, just swap. */
>> nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
>> @@ -423,6 +440,68 @@ nouveau_dri2_vblank_handler(int fd, unsigned
>> int frame,
>> }
>> }
>>
>> +void
>> +nouveau_dri2_flip_event_handler(unsigned int frame, unsigned int
>> tv_sec,
>> + unsigned int tv_usec, void *event_data)
>> +{
>> + struct nouveau_dri2_vblank_state *flip = event_data;
>> + DrawablePtr draw;
>> + ScreenPtr screen;
>> + ScrnInfoPtr scrn;
>> + int status;
>> + PixmapPtr pixmap;
>> +
>> + status = dixLookupDrawable(&draw, flip->draw, serverClient,
>> + M_ANY, DixWriteAccess);
>> + if (status != Success) {
>> + free(flip);
>> + return;
>> + }
>> +
>> + screen = draw->pScreen;
>> + scrn = xf86Screens[screen->myNum];
>> +
>> + pixmap = screen->GetScreenPixmap(screen);
>> + xf86DrvMsg(scrn->scrnIndex, X_INFO,
>> + "%s:%d fevent[%p] width %d pitch %d (/4 %d)\n",
>> + __func__, __LINE__, flip, pixmap->drawable.width,
>> + pixmap->devKind, pixmap->devKind/4);
>> +
>> + /* We assume our flips arrive in order, so we don't check the
>> frame */
>> + switch (flip->action) {
>> + case SWAP:
>> + /* Check for too small vblank count of pageflip completion,
>> + * taking wraparound into account. This usually means some
>> + * defective kms pageflip completion, causing wrong (msc, ust)
>> + * return values and possible visual corruption.
>> + * Skip test for frame == 0, as this is a valid constant value
>> + * reported by all Linux kernels at least up to Linux 3.0.
>> + */
>> + if ((frame != 0) &&
>> + (frame < flip->frame) && (flip->frame - frame < 5)) {
>> + xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> + "%s: Pageflip has impossible msc %d < target_msc %d\n",
>> + __func__, frame, flip->frame);
>> + /* All-Zero values signal failure of (msc, ust)
>> + * timestamping to client.
>> + */
>> + frame = tv_sec = tv_usec = 0;
>> + }
>> +
>> + DRI2SwapComplete(flip->client, draw, frame, tv_sec, tv_usec,
>> + DRI2_FLIP_COMPLETE, flip->func,
>> + flip->data);
>> + break;
>> + default:
>> + xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> + "%s: unknown vblank event received\n", __func__);
>> + /* Unknown type */
>> + break;
>> + }
>> +
>> + free(flip);
>> +}
>> +
>> Bool
>> nouveau_dri2_init(ScreenPtr pScreen)
>> {
>> diff --git a/src/nv_proto.h b/src/nv_proto.h
>> index 2e4fce0..2bd2ac7 100644
>> --- a/src/nv_proto.h
>> +++ b/src/nv_proto.h
>> @@ -7,7 +7,8 @@ void drmmode_adjust_frame(ScrnInfoPtr pScrn, int
>> x, int y, int flags);
>> void drmmode_remove_fb(ScrnInfoPtr pScrn);
>> Bool drmmode_cursor_init(ScreenPtr pScreen);
>> void drmmode_fbcon_copy(ScreenPtr pScreen);
>> -Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void
>> *priv);
>> +Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
>> + unsigned int ref_crtc_hw_id);
>> void drmmode_screen_init(ScreenPtr pScreen);
>> void drmmode_screen_fini(ScreenPtr pScreen);
>>
>> @@ -26,6 +27,8 @@ Bool nouveau_allocate_surface(ScrnInfoPtr scrn,
>> int width, int height,
>> void nouveau_dri2_vblank_handler(int fd, unsigned int frame,
>> unsigned int tv_sec, unsigned int tv_usec,
>> void *event_data);
>> +void nouveau_dri2_flip_event_handler(unsigned int frame, unsigned
>> int tv_sec,
>> + unsigned int tv_usec, void *event_data);
>> Bool nouveau_dri2_init(ScreenPtr pScreen);
>> void nouveau_dri2_fini(ScreenPtr pScreen);
*********************************************************************
Mario Kleiner
Max Planck Institute for Biological Cybernetics
Spemannstr. 38
72076 Tuebingen
Germany
e-mail: mario.kleiner at tuebingen.mpg.de
office: +49 (0)7071/601-1623
fax: +49 (0)7071/601-616
www: http://www.kyb.tuebingen.mpg.de/~kleinerm
*********************************************************************
"For a successful technology, reality must take precedence
over public relations, for Nature cannot be fooled."
(Richard Feynman)
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