fb: fix fast-path blt detection

Backport of this commit: commit a2880699e8f1f576e1a48ebf25e8982463323f84 Author: Keith Packard <keithp@keithp.com> Date: Tue Mar 25 08:21:16 2014 -0700 fb: fix fast-path blt detection The width parameter is used to disable the blit fast-path (memcpy) when source and destination rows overlap in memory. This check was added in [0]. Unfortunately, the calculation to determine if source and destination lines overlapped was incorrect: (1) it converts width from pixels to bytes, but width is actually in bits, not pixels. (2) it adds this byte offset to dst/srcLine, which implicitly converts the offset from bytes to sizeof(FbBits). Fix both of these by converting addresses to byte pointers and width to bytes and doing comparisons on the resulting byte address. For example: A 32-bpp 1366 pixel-wide row will have width = 1366 * 32 = 43712 bits bpp = 32 (bpp >> 3) = 4 width * (bpp >> 3) = 174848 FbBits (FbBits *)width => 699392 bytes So, "careful" was true if the destination line was within 699392 bytes, instead of just within its 1366 * 4 = 5464 byte row. This bug causes us to take the slow path for large non-overlapping rows that are "close" in memory. As a data point, XGetImage(1366x768) on my ARM chromebook was taking ~140 ms, but with this fixed, it now takes about 60 ms. XGetImage() -> exaGetImage() -> fbGetImage -> fbBlt() [0] commit e32cc0b4c85c78cd8743a6e1680dcc79054b57ce Author: Adam Jackson <ajax@redhat.com> Date: Thu Apr 21 16:37:11 2011 -0400 fb: Fix memcpy abuse The memcpy fast path implicitly assumes that the copy walks left-to-right. That's not something memcpy guarantees, and newer glibc on some processors will indeed break that assumption. Since we walk a line at a time, check the source and destination against the width of the blit to determine whether we can be sloppy enough to allow memcpy. (Having done this, we can remove the check for !reverse as well.) v3: Convert to byte units This first checks to make sure the blt is byte aligned, converts all of the data to byte units and then compares for byte address range overlap between source and dest. Signed-off-by: Keith Packard <keithp@keithp.com> Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>

fb: fix fast-path blt detection
034228d7 · Ulrich Sibiller · Mike Gabriel · 020ef045 · 034228d7
Commit 034228d7 authored Dec 18, 2018 by Ulrich Sibiller Committed by Mike Gabriel Dec 19, 2018
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Showing with 34 additions and 27 deletions

fbblt.c nx-X11/programs/Xserver/fb/fbblt.c +34 -27

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--- a/nx-X11/programs/Xserver/fb/fbblt.c
+++ b/nx-X11/programs/Xserver/fb/fbblt.c
@@ -67,9 +67,42 @@ fbBlt (FbBits   *srcLine,
    int	    n, nmiddle;
    Bool    destInvarient;
    int	    startbyte, endbyte;
-    int     careful;
+
    FbDeclareMergeRop ();

+    if (alu == GXcopy && pm == FB_ALLONES &&
+        !(srcX & 7) && !(dstX & 7) && !(width & 7))
+    {
+        CARD8           *src_byte = (CARD8 *) srcLine + (srcX >> 3);
+        CARD8           *dst_byte = (CARD8 *) dstLine + (dstX >> 3);
+        FbStride        src_byte_stride = srcStride << (FB_SHIFT - 3);
+        FbStride        dst_byte_stride = dstStride << (FB_SHIFT - 3);
+        int             width_byte = (width >> 3);
+
+        /* Make sure there's no overlap; we can't use memcpy in that
+         * case as it's not well defined, so fall through to the
+         * general code
+         */
+        if (src_byte + width_byte <= dst_byte ||
+            dst_byte + width_byte <= src_byte)
+        {
+            int i;
+
+            if (!upsidedown)
+                for (i = 0; i < height; i++)
+                    memcpy(dst_byte + i * dst_byte_stride,
+                           src_byte + i * src_byte_stride,
+                           width_byte);
+            else
+                for (i = height - 1; i >= 0; i--)
+                    memcpy(dst_byte + i * dst_byte_stride,
+                           src_byte + i * src_byte_stride,
+                           width_byte);
+
+            return;
+        }
+    }
+
 #ifdef FB_24BIT
    if (bpp == 24 && !FbCheck24Pix (pm))
    {
@@ -79,32 +112,6 @@ fbBlt (FbBits   *srcLine,
    }
 #endif

-    careful = !((srcLine < dstLine && srcLine + width * (bpp>>3) > dstLine) ||
-                (dstLine < srcLine && dstLine + width * (bpp>>3) > srcLine)) ||
-              (bpp & 7);
-
-    if (alu == GXcopy && pm == FB_ALLONES && !careful &&
-            !(srcX & 7) && !(dstX & 7) && !(width & 7)) {
-        int i;
-        CARD8 *src = (CARD8 *) srcLine;
-        CARD8 *dst = (CARD8 *) dstLine;
-
-        srcStride *= sizeof(FbBits);
-        dstStride *= sizeof(FbBits);
-        width >>= 3;
-        src += (srcX >> 3);
-        dst += (dstX >> 3);
-
-        if (!upsidedown)
-            for (i = 0; i < height; i++)
-                memcpy(dst + i * dstStride, src + i * srcStride, width);
-        else
-            for (i = height - 1; i >= 0; i--)
-                memcpy(dst + i * dstStride, src + i * srcStride, width);
-
-        return;
-    }
-
    FbInitializeMergeRop(alu, pm);
    destInvarient = FbDestInvarientMergeRop();
    if (upsidedown)