exa: A simple 3rd backend implementation.

- Based on driver pixmaps with some changes (completely transparent to driver). - It helps with the problem of known software fallbacks, such as trapezoids. - exaDoMigration is now called for all cases that provide a do_migration hook. - exa_migration.c is renamed to exa_migration_classic.c
2026-10-14 00:01:20 +00:00 · 2009-08-01 19:19:19 +02:00 · 2009-08-01 19:19:19 +02:00 · 03ecb164f2
commit 03ecb164f2
parent ac7ac913fd
10 changed files with 460 additions and 58 deletions
--- a/exa/exa_migration_classic.c
+++ b/exa/exa_migration_classic.c
@ -0,0 +1,720 @@
+/*
+ * Copyright © 2006 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * Authors:
+ *    Eric Anholt <eric@anholt.net>
+ *    Michel Dänzer <michel@tungstengraphics.com>
+ *
+ */
+
+#ifdef HAVE_DIX_CONFIG_H
+#include <dix-config.h>
+#endif
+
+#include <string.h>
+
+#include "exa_priv.h"
+#include "exa.h"
+
+#if DEBUG_MIGRATE
+#define DBG_MIGRATE(a) ErrorF a
+#else
+#define DBG_MIGRATE(a)
+#endif
+
+/**
+ * The fallback path for UTS/DFS failing is to just memcpy.  exaCopyDirtyToSys
+ * and exaCopyDirtyToFb both needed to do this loop.
+ */
+static void
+exaMemcpyBox (PixmapPtr pPixmap, BoxPtr pbox, CARD8 *src, int src_pitch,
+	      CARD8 *dst, int dst_pitch)
+ {
+    int i, cpp = pPixmap->drawable.bitsPerPixel / 8;
+    int bytes = (pbox->x2 - pbox->x1) * cpp;
+
+    src += pbox->y1 * src_pitch + pbox->x1 * cpp;
+    dst += pbox->y1 * dst_pitch + pbox->x1 * cpp;
+
+    for (i = pbox->y2 - pbox->y1; i; i--) {
+	memcpy (dst, src, bytes);
+	src += src_pitch;
+	dst += dst_pitch;
+    }
+}
+
+/**
+ * Returns TRUE if the pixmap is dirty (has been modified in its current
+ * location compared to the other), or lacks a private for tracking
+ * dirtiness.
+ */
+static Bool
+exaPixmapIsDirty (PixmapPtr pPix)
+{
+    ExaPixmapPriv (pPix);
+
+    if (pExaPixmap == NULL)
+	EXA_FatalErrorDebugWithRet(("EXA bug: exaPixmapIsDirty was called on a non-exa pixmap.\n"), TRUE);
+
+    return REGION_NOTEMPTY (pScreen, DamageRegion(pExaPixmap->pDamage)) ||
+	!REGION_EQUAL(pScreen, &pExaPixmap->validSys, &pExaPixmap->validFB);
+}
+
+/**
+ * Returns TRUE if the pixmap is either pinned in FB, or has a sufficient score
+ * to be considered "should be in framebuffer".  That's just anything that has
+ * had more acceleration than fallbacks, or has no score yet.
+ *
+ * Only valid if using a migration scheme that tracks score.
+ */
+static Bool
+exaPixmapShouldBeInFB (PixmapPtr pPix)
+{
+    ExaPixmapPriv (pPix);
+
+    if (exaPixmapIsPinned (pPix))
+	return TRUE;
+
+    return pExaPixmap->score >= 0;
+}
+
+/**
+ * If the pixmap is currently dirty, this copies at least the dirty area from
+ * FB to system or vice versa.  Both areas must be allocated.
+ */
+static void
+exaCopyDirty(ExaMigrationPtr migrate, RegionPtr pValidDst, RegionPtr pValidSrc,
+	     Bool (*transfer) (PixmapPtr pPix, int x, int y, int w, int h,
+			       char *sys, int sys_pitch), CARD8 *fallback_src,
+	     CARD8 *fallback_dst, int fallback_srcpitch, int fallback_dstpitch,
+	     int fallback_index, void (*sync) (ScreenPtr pScreen))
+{
+    PixmapPtr pPixmap = migrate->pPix;
+    ExaPixmapPriv (pPixmap);
+    RegionPtr damage = DamageRegion (pExaPixmap->pDamage);
+    RegionRec CopyReg;
+    Bool save_offscreen;
+    int save_pitch;
+    BoxPtr pBox;
+    int nbox;
+    Bool access_prepared = FALSE;
+    Bool need_sync = FALSE;
+
+    /* Damaged bits are valid in current copy but invalid in other one */
+    if (exaPixmapIsOffscreen(pPixmap)) {
+	REGION_UNION(pScreen, &pExaPixmap->validFB, &pExaPixmap->validFB,
+		     damage);
+	REGION_SUBTRACT(pScreen, &pExaPixmap->validSys, &pExaPixmap->validSys,
+			damage);
+    } else {
+	REGION_UNION(pScreen, &pExaPixmap->validSys, &pExaPixmap->validSys,
+		     damage);
+	REGION_SUBTRACT(pScreen, &pExaPixmap->validFB, &pExaPixmap->validFB,
+			damage);
+    }
+
+    REGION_EMPTY(pScreen, damage);
+
+    /* Copy bits valid in source but not in destination */
+    REGION_NULL(pScreen, &CopyReg);
+    REGION_SUBTRACT(pScreen, &CopyReg, pValidSrc, pValidDst);
+
+    if (migrate->as_dst) {
+	ExaScreenPriv (pPixmap->drawable.pScreen);
+
+	/* XXX: The pending damage region will be marked as damaged after the
+	 * operation, so it should serve as an upper bound for the region that
+	 * needs to be synchronized for the operation. Unfortunately, this
+	 * causes corruption in some cases, e.g. when starting compiz. See
+	 * https://bugs.freedesktop.org/show_bug.cgi?id=12916 .
+	 */
+	if (pExaScr->optimize_migration) {
+	    RegionPtr pending_damage = DamagePendingRegion(pExaPixmap->pDamage);
+
+#if DEBUG_MIGRATE
+	    if (REGION_NIL(pending_damage)) {
+		static Bool firsttime = TRUE;
+
+		if (firsttime) {
+		    ErrorF("%s: Pending damage region empty!\n", __func__);
+		    firsttime = FALSE;
+		}
+	    }
+#endif
+
+	    /* Try to prevent destination valid region from growing too many
+	     * rects by filling it up to the extents of the union of the
+	     * destination valid region and the pending damage region.
+	     */
+	    if (REGION_NUM_RECTS(pValidDst) > 10) {
+		BoxRec box;
+		BoxPtr pValidExt, pDamageExt;
+		RegionRec closure;
+
+		pValidExt = REGION_EXTENTS(pScreen, pValidDst);
+		pDamageExt = REGION_EXTENTS(pScreen, pending_damage);
+
+		box.x1 = min(pValidExt->x1, pDamageExt->x1);
+		box.y1 = min(pValidExt->y1, pDamageExt->y1);
+		box.x2 = max(pValidExt->x2, pDamageExt->x2);
+		box.y2 = max(pValidExt->y2, pDamageExt->y2);
+
+		REGION_INIT(pScreen, &closure, &box, 0);
+		REGION_INTERSECT(pScreen, &CopyReg, &CopyReg, &closure);
+	    } else
+		REGION_INTERSECT(pScreen, &CopyReg, &CopyReg, pending_damage);
+	}
+
+	/* The caller may provide a region to be subtracted from the calculated
+	 * dirty region. This is to avoid migration of bits that don't
+	 * contribute to the result of the operation.
+	 */
+	if (migrate->pReg)
+	    REGION_SUBTRACT(pScreen, &CopyReg, &CopyReg, migrate->pReg);
+    } else {
+	/* The caller may restrict the region to be migrated for source pixmaps
+	 * to what's relevant for the operation.
+	 */
+	if (migrate->pReg)
+	    REGION_INTERSECT(pScreen, &CopyReg, &CopyReg, migrate->pReg);
+    }
+
+    pBox = REGION_RECTS(&CopyReg);
+    nbox = REGION_NUM_RECTS(&CopyReg);
+
+    save_offscreen = pExaPixmap->offscreen;
+    save_pitch = pPixmap->devKind;
+    pExaPixmap->offscreen = TRUE;
+    pPixmap->devKind = pExaPixmap->fb_pitch;
+
+    while (nbox--) {
+	pBox->x1 = max(pBox->x1, 0);
+	pBox->y1 = max(pBox->y1, 0);
+	pBox->x2 = min(pBox->x2, pPixmap->drawable.width);
+	pBox->y2 = min(pBox->y2, pPixmap->drawable.height);
+
+	if (pBox->x1 >= pBox->x2 || pBox->y1 >= pBox->y2)
+	    continue;
+
+	if (!transfer || !transfer (pPixmap,
+				    pBox->x1, pBox->y1,
+				    pBox->x2 - pBox->x1,
+				    pBox->y2 - pBox->y1,
+				    (char *) (pExaPixmap->sys_ptr
+				    + pBox->y1 * pExaPixmap->sys_pitch
+				    + pBox->x1 * pPixmap->drawable.bitsPerPixel / 8),
+				    pExaPixmap->sys_pitch))
+	{
+	    if (!access_prepared) {
+		ExaDoPrepareAccess(&pPixmap->drawable, fallback_index);
+		access_prepared = TRUE;
+	    }
+	    exaMemcpyBox (pPixmap, pBox,
+			  fallback_src, fallback_srcpitch,
+			  fallback_dst, fallback_dstpitch);
+	} else
+	    need_sync = TRUE;
+
+	pBox++;
+    }
+
+    if (access_prepared)
+	exaFinishAccess(&pPixmap->drawable, fallback_index);
+    else if (need_sync && sync)
+	sync (pPixmap->drawable.pScreen);
+
+    pExaPixmap->offscreen = save_offscreen;
+    pPixmap->devKind = save_pitch;
+
+    /* Try to prevent source valid region from growing too many rects by
+     * removing parts of it which are also in the destination valid region.
+     * Removing anything beyond that would lead to data loss.
+     */
+    if (REGION_NUM_RECTS(pValidSrc) > 20)
+	REGION_SUBTRACT(pScreen, pValidSrc, pValidSrc, pValidDst);
+
+    /* The copied bits are now valid in destination */
+    REGION_UNION(pScreen, pValidDst, pValidDst, &CopyReg);
+
+    REGION_UNINIT(pScreen, &CopyReg);
+}
+
+/**
+ * If the pixmap is currently dirty, this copies at least the dirty area from
+ * the framebuffer  memory copy to the system memory copy.  Both areas must be
+ * allocated.
+ */
+static void
+exaCopyDirtyToSys (ExaMigrationPtr migrate)
+{
+    PixmapPtr pPixmap = migrate->pPix;
+    ExaScreenPriv (pPixmap->drawable.pScreen);
+    ExaPixmapPriv (pPixmap);
+
+    exaCopyDirty(migrate, &pExaPixmap->validSys, &pExaPixmap->validFB,
+		 pExaScr->info->DownloadFromScreen, pExaPixmap->fb_ptr,
+		 pExaPixmap->sys_ptr, pExaPixmap->fb_pitch,
+		 pExaPixmap->sys_pitch, EXA_PREPARE_SRC, exaWaitSync);
+}
+
+/**
+ * If the pixmap is currently dirty, this copies at least the dirty area from
+ * the system memory copy to the framebuffer memory copy.  Both areas must be
+ * allocated.
+ */
+static void
+exaCopyDirtyToFb (ExaMigrationPtr migrate)
+{
+    PixmapPtr pPixmap = migrate->pPix;
+    ExaScreenPriv (pPixmap->drawable.pScreen);
+    ExaPixmapPriv (pPixmap);
+
+    exaCopyDirty(migrate, &pExaPixmap->validFB, &pExaPixmap->validSys,
+		 pExaScr->info->UploadToScreen, pExaPixmap->sys_ptr,
+		 pExaPixmap->fb_ptr, pExaPixmap->sys_pitch,
+		 pExaPixmap->fb_pitch, EXA_PREPARE_DEST, NULL);
+}
+
+/**
+ * Allocates a framebuffer copy of the pixmap if necessary, and then copies
+ * any necessary pixmap data into the framebuffer copy and points the pixmap at
+ * it.
+ *
+ * Note that when first allocated, a pixmap will have FALSE dirty flag.
+ * This is intentional because pixmap data starts out undefined.  So if we move
+ * it in due to the first operation against it being accelerated, it will have
+ * undefined framebuffer contents that we didn't have to upload.  If we do
+ * moveouts (and moveins) after the first movein, then we will only have to copy
+ * back and forth if the pixmap was written to after the last synchronization of
+ * the two copies.  Then, at exaPixmapSave (when the framebuffer copy goes away)
+ * we mark the pixmap dirty, so that the next exaMoveInPixmap will actually move
+ * all the data, since it's almost surely all valid now.
+ */
+static void
+exaDoMoveInPixmap (ExaMigrationPtr migrate)
+{
+    PixmapPtr pPixmap = migrate->pPix;
+    ScreenPtr pScreen = pPixmap->drawable.pScreen;
+    ExaScreenPriv (pScreen);
+    ExaPixmapPriv (pPixmap);
+
+    /* If we're VT-switched away, no touching card memory allowed. */
+    if (pExaScr->swappedOut)
+	return;
+
+    /* If we're not allowed to move, then fail. */
+    if (exaPixmapIsPinned(pPixmap))
+	return;
+
+    /* Don't migrate in pixmaps which are less than 8bpp.  This avoids a lot of
+     * fragility in EXA, and <8bpp is probably not used enough any more to care
+     * (at least, not in acceleratd paths).
+     */
+    if (pPixmap->drawable.bitsPerPixel < 8)
+	return;
+
+    if (pExaPixmap->accel_blocked)
+	return;
+
+    if (pExaPixmap->area == NULL) {
+	pExaPixmap->area =
+	    exaOffscreenAlloc (pScreen, pExaPixmap->fb_size,
+			       pExaScr->info->pixmapOffsetAlign, FALSE,
+                               exaPixmapSave, (pointer) pPixmap);
+	if (pExaPixmap->area == NULL)
+	    return;
+
+	pExaPixmap->fb_ptr = (CARD8 *) pExaScr->info->memoryBase +
+				       pExaPixmap->area->offset;
+    }
+
+    exaCopyDirtyToFb (migrate);
+
+    if (exaPixmapIsOffscreen(pPixmap))
+	return;
+
+    DBG_MIGRATE (("-> %p (0x%x) (%dx%d) (%c)\n", pPixmap,
+		  (ExaGetPixmapPriv(pPixmap)->area ?
+                   ExaGetPixmapPriv(pPixmap)->area->offset : 0),
+		  pPixmap->drawable.width,
+		  pPixmap->drawable.height,
+		  exaPixmapIsDirty(pPixmap) ? 'd' : 'c'));
+
+    pExaPixmap->offscreen = TRUE;
+
+    pPixmap->devKind = pExaPixmap->fb_pitch;
+    pPixmap->drawable.serialNumber = NEXT_SERIAL_NUMBER;
+}
+
+void
+exaMoveInPixmap (PixmapPtr pPixmap)
+{
+    static ExaMigrationRec migrate = { .as_dst = FALSE, .as_src = TRUE,
+				       .pReg = NULL };
+
+    migrate.pPix = pPixmap;
+    exaDoMoveInPixmap (&migrate);
+}
+
+/**
+ * Switches the current active location of the pixmap to system memory, copying
+ * updated data out if necessary.
+ */
+static void
+exaDoMoveOutPixmap (ExaMigrationPtr migrate)
+{
+    PixmapPtr pPixmap = migrate->pPix;
+    ExaPixmapPriv (pPixmap);
+
+    if (!pExaPixmap->area || exaPixmapIsPinned(pPixmap))
+	return;
+
+    exaCopyDirtyToSys (migrate);
+
+    if (exaPixmapIsOffscreen(pPixmap)) {
+
+	DBG_MIGRATE (("<- %p (%p) (%dx%d) (%c)\n", pPixmap,
+		      (void*)(ExaGetPixmapPriv(pPixmap)->area ?
+			      ExaGetPixmapPriv(pPixmap)->area->offset : 0),
+		      pPixmap->drawable.width,
+		      pPixmap->drawable.height,
+		      exaPixmapIsDirty(pPixmap) ? 'd' : 'c'));
+
+	pExaPixmap->offscreen = FALSE;
+
+	pPixmap->devKind = pExaPixmap->sys_pitch;
+	pPixmap->drawable.serialNumber = NEXT_SERIAL_NUMBER;
+    }
+}
+
+void
+exaMoveOutPixmap (PixmapPtr pPixmap)
+{
+    static ExaMigrationRec migrate = { .as_dst = FALSE, .as_src = TRUE,
+				       .pReg = NULL };
+
+    migrate.pPix = pPixmap;
+    exaDoMoveOutPixmap (&migrate);
+}
+
+
+/**
+ * Copies out important pixmap data and removes references to framebuffer area.
+ * Called when the memory manager decides it's time to kick the pixmap out of
+ * framebuffer entirely.
+ */
+void
+exaPixmapSave (ScreenPtr pScreen, ExaOffscreenArea *area)
+{
+    PixmapPtr pPixmap = area->privData;
+    ExaPixmapPriv(pPixmap);
+
+    exaMoveOutPixmap(pPixmap);
+
+    pExaPixmap->fb_ptr = NULL;
+    pExaPixmap->area = NULL;
+
+    /* Mark all FB bits as invalid, so all valid system bits get copied to FB
+     * next time */
+    REGION_EMPTY(pPixmap->drawable.pScreen, &pExaPixmap->validFB);
+}
+
+/**
+ * For the "greedy" migration scheme, pushes the pixmap toward being located in
+ * framebuffer memory.
+ */
+static void
+exaMigrateTowardFb (ExaMigrationPtr migrate)
+{
+    PixmapPtr pPixmap = migrate->pPix;
+    ExaPixmapPriv (pPixmap);
+
+    if (pExaPixmap->score == EXA_PIXMAP_SCORE_PINNED) {
+	DBG_MIGRATE(("UseScreen: not migrating pinned pixmap %p\n",
+		     (pointer)pPixmap));
+	return;
+    }
+
+    DBG_MIGRATE(("UseScreen %p score %d\n",
+		 (pointer)pPixmap, pExaPixmap->score));
+
+    if (pExaPixmap->score == EXA_PIXMAP_SCORE_INIT) {
+	exaDoMoveInPixmap(migrate);
+	pExaPixmap->score = 0;
+    }
+
+    if (pExaPixmap->score < EXA_PIXMAP_SCORE_MAX)
+	pExaPixmap->score++;
+
+    if (pExaPixmap->score >= EXA_PIXMAP_SCORE_MOVE_IN &&
+	!exaPixmapIsOffscreen(pPixmap))
+    {
+	exaDoMoveInPixmap(migrate);
+    }
+
+    if (exaPixmapIsOffscreen(pPixmap)) {
+	exaCopyDirtyToFb (migrate);
+	ExaOffscreenMarkUsed (pPixmap);
+    } else
+	exaCopyDirtyToSys (migrate);
+}
+
+/**
+ * For the "greedy" migration scheme, pushes the pixmap toward being located in
+ * system memory.
+ */
+static void
+exaMigrateTowardSys (ExaMigrationPtr migrate)
+{
+    PixmapPtr pPixmap = migrate->pPix;
+    ExaPixmapPriv (pPixmap);
+
+    DBG_MIGRATE(("UseMem: %p score %d\n", (pointer)pPixmap, pExaPixmap->score));
+
+    if (pExaPixmap->score == EXA_PIXMAP_SCORE_PINNED)
+	return;
+
+    if (pExaPixmap->score == EXA_PIXMAP_SCORE_INIT)
+	pExaPixmap->score = 0;
+
+    if (pExaPixmap->score > EXA_PIXMAP_SCORE_MIN)
+	pExaPixmap->score--;
+
+    if (pExaPixmap->score <= EXA_PIXMAP_SCORE_MOVE_OUT && pExaPixmap->area)
+	exaDoMoveOutPixmap(migrate);
+
+    if (exaPixmapIsOffscreen(pPixmap)) {
+	exaCopyDirtyToFb (migrate);
+	ExaOffscreenMarkUsed (pPixmap);
+    } else
+	exaCopyDirtyToSys (migrate);
+}
+
+/**
+ * If the pixmap has both a framebuffer and system memory copy, this function
+ * asserts that both of them are the same.
+ */
+static Bool
+exaAssertNotDirty (PixmapPtr pPixmap)
+{
+    ExaPixmapPriv (pPixmap);
+    CARD8 *dst, *src;
+    RegionRec ValidReg;
+    int dst_pitch, src_pitch, cpp, y, nbox, save_pitch;
+    BoxPtr pBox;
+    Bool ret = TRUE, save_offscreen;
+
+    if (exaPixmapIsPinned(pPixmap) || pExaPixmap->area == NULL)
+	return ret;
+
+    REGION_NULL(pScreen, &ValidReg);
+    REGION_INTERSECT(pScreen, &ValidReg, &pExaPixmap->validFB,
+		     &pExaPixmap->validSys);
+    nbox = REGION_NUM_RECTS(&ValidReg);
+
+    if (!nbox)
+	goto out;
+
+    pBox = REGION_RECTS(&ValidReg);
+
+    dst_pitch = pExaPixmap->sys_pitch;
+    src_pitch = pExaPixmap->fb_pitch;
+    cpp = pPixmap->drawable.bitsPerPixel / 8;
+
+    save_offscreen = pExaPixmap->offscreen;
+    save_pitch = pPixmap->devKind;
+    pExaPixmap->offscreen = TRUE;
+    pPixmap->devKind = pExaPixmap->fb_pitch;
+
+    if (!ExaDoPrepareAccess(&pPixmap->drawable, EXA_PREPARE_SRC))
+	goto skip;
+
+    while (nbox--) {
+	    int rowbytes;
+
+	    pBox->x1 = max(pBox->x1, 0);
+	    pBox->y1 = max(pBox->y1, 0);
+	    pBox->x2 = min(pBox->x2, pPixmap->drawable.width);
+	    pBox->y2 = min(pBox->y2, pPixmap->drawable.height);
+
+	    if (pBox->x1 >= pBox->x2 || pBox->y1 >= pBox->y2)
+		continue;
+
+	    rowbytes = (pBox->x2 - pBox->x1) * cpp;
+	    src = (CARD8 *) pPixmap->devPrivate.ptr + pBox->y1 * src_pitch + pBox->x1 * cpp;
+	    dst = pExaPixmap->sys_ptr + pBox->y1 * dst_pitch + pBox->x1 * cpp;
+
+	    for (y = pBox->y1; y < pBox->y2;
+		 y++, src += src_pitch, dst += dst_pitch) {
+		if (memcmp(dst, src, rowbytes) != 0) {
+		    ret = FALSE;
+		    exaPixmapDirty(pPixmap, pBox->x1, pBox->y1, pBox->x2,
+				   pBox->y2);
+		    break;
+		}
+	    }
+    }
+
+skip:
+    exaFinishAccess(&pPixmap->drawable, EXA_PREPARE_SRC);
+
+    pExaPixmap->offscreen = save_offscreen;
+    pPixmap->devKind = save_pitch;
+
+out:
+    REGION_UNINIT(pScreen, &ValidReg);
+    return ret;
+}
+
+/**
+ * Performs migration of the pixmaps according to the operation information
+ * provided in pixmaps and can_accel and the migration scheme chosen in the
+ * config file.
+ */
+void
+exaDoMigration_classic (ExaMigrationPtr pixmaps, int npixmaps, Bool can_accel)
+{
+    ScreenPtr pScreen = pixmaps[0].pPix->drawable.pScreen;
+    ExaScreenPriv(pScreen);
+    int i, j;
+
+    /* If this debugging flag is set, check each pixmap for whether it is marked
+     * as clean, and if so, actually check if that's the case.  This should help
+     * catch issues with failing to mark a drawable as dirty.  While it will
+     * catch them late (after the operation happened), it at least explains what
+     * went wrong, and instrumenting the code to find what operation happened
+     * to the pixmap last shouldn't be hard.
+     */
+    if (pExaScr->checkDirtyCorrectness) {
+	for (i = 0; i < npixmaps; i++) {
+	    if (!exaPixmapIsDirty (pixmaps[i].pPix) &&
+		!exaAssertNotDirty (pixmaps[i].pPix))
+		ErrorF("%s: Pixmap %d dirty but not marked as such!\n", __func__, i);
+	}
+    }
+    /* If anything is pinned in system memory, we won't be able to
+     * accelerate.
+     */
+    for (i = 0; i < npixmaps; i++) {
+	if (exaPixmapIsPinned (pixmaps[i].pPix) &&
+	    !exaPixmapIsOffscreen (pixmaps[i].pPix))
+	{
+	    EXA_FALLBACK(("Pixmap %p (%dx%d) pinned in sys\n", pixmaps[i].pPix,
+		      pixmaps[i].pPix->drawable.width,
+		      pixmaps[i].pPix->drawable.height));
+	    can_accel = FALSE;
+	    break;
+	}
+    }
+
+    if (pExaScr->migration == ExaMigrationSmart) {
+	/* If we've got something as a destination that we shouldn't cause to
+	 * become newly dirtied, take the unaccelerated route.
+	 */
+	for (i = 0; i < npixmaps; i++) {
+	    if (pixmaps[i].as_dst && !exaPixmapShouldBeInFB (pixmaps[i].pPix) &&
+		!exaPixmapIsDirty (pixmaps[i].pPix))
+	    {
+		for (i = 0; i < npixmaps; i++) {
+		    if (!exaPixmapIsDirty (pixmaps[i].pPix))
+			exaDoMoveOutPixmap (pixmaps + i);
+		}
+		return;
+	    }
+	}
+
+	/* If we aren't going to accelerate, then we migrate everybody toward
+	 * system memory, and kick out if it's free.
+	 */
+	if (!can_accel) {
+	    for (i = 0; i < npixmaps; i++) {
+		exaMigrateTowardSys (pixmaps + i);
+		if (!exaPixmapIsDirty (pixmaps[i].pPix))
+		    exaDoMoveOutPixmap (pixmaps + i);
+	    }
+	    return;
+	}
+
+	/* Finally, the acceleration path.  Move them all in. */
+	for (i = 0; i < npixmaps; i++) {
+	    exaMigrateTowardFb(pixmaps + i);
+	    exaDoMoveInPixmap(pixmaps + i);
+	}
+    } else if (pExaScr->migration == ExaMigrationGreedy) {
+	/* If we can't accelerate, either because the driver can't or because one of
+	 * the pixmaps is pinned in system memory, then we migrate everybody toward
+	 * system memory.
+	 *
+	 * We also migrate toward system if all pixmaps involved are currently in
+	 * system memory -- this can mitigate thrashing when there are significantly
+	 * more pixmaps active than would fit in memory.
+	 *
+	 * If not, then we migrate toward FB so that hopefully acceleration can
+	 * happen.
+	 */
+	if (!can_accel) {
+	    for (i = 0; i < npixmaps; i++)
+		exaMigrateTowardSys (pixmaps + i);
+	    return;
+	}
+
+	for (i = 0; i < npixmaps; i++) {
+	    if (exaPixmapIsOffscreen(pixmaps[i].pPix)) {
+		/* Found one in FB, so move all to FB. */
+		for (j = 0; j < npixmaps; j++)
+		    exaMigrateTowardFb(pixmaps + i);
+		return;
+	    }
+	}
+
+	/* Nobody's in FB, so move all away from FB. */
+	for (i = 0; i < npixmaps; i++)
+	    exaMigrateTowardSys(pixmaps + i);
+    } else if (pExaScr->migration == ExaMigrationAlways) {
+	/* Always move the pixmaps out if we can't accelerate.  If we can
+	 * accelerate, try to move them all in.  If that fails, then move them
+	 * back out.
+	 */
+	if (!can_accel) {
+	    for (i = 0; i < npixmaps; i++)
+		exaDoMoveOutPixmap(pixmaps + i);
+	    return;
+	}
+
+	/* Now, try to move them all into FB */
+	for (i = 0; i < npixmaps; i++) {
+	    exaDoMoveInPixmap(pixmaps + i);
+	}
+
+	/* If we couldn't fit everything in, abort */
+	for (i = 0; i < npixmaps; i++) {
+	    if (!exaPixmapIsOffscreen(pixmaps[i].pPix)) {
+		return;
+	    }
+	}
+
+	/* Yay, everything's offscreen, mark memory as used */
+	for (i = 0; i < npixmaps; i++) {
+	    ExaOffscreenMarkUsed (pixmaps[i].pPix);
+	}
+    }
+}