Add a shadow VRAM to track changes to the real VRAM. When the guest

OS was given write access to the VRAM the device model tracked all
VRAM changes by updating the entire screen on every output loop,
causing significant overhead (a CPU bound loop in a guest slows down
by about 35%) and significant mouse latency (VNC uses the same data
path for mouse events and video updates).  With the shadow VRAM only
modified pages need to be updated and the comparison of the shadow
VRAM to the real VRAM only adds ~4% overhead while eliminating the
mouse latencies.

Signed-off-by: Don Dugger <donald.d.dugger@intel.com>

diff --git a/tools/ioemu/hw/vga.c b/tools/ioemu/hw/vga.c
index b74498456cc0a26e749225a85e84c494146d3239..51980ba79caee6a51edcbab2874363f0c0b5a937 100644 (file)
--- a/tools/ioemu/hw/vga.c
+++ b/tools/ioemu/hw/vga.c
@@ -1340,6 +1340,99 @@ void vga_invalidate_scanlines(VGAState *s, int y1, int y2)
     }
 }
 
+extern inline int cmp_vram(VGAState *s, int offset, int n)
+{
+    long *vp, *sp;
+
+    if (s->vram_shadow == NULL)
+        return 1;
+    vp = (long *)(s->vram_ptr + offset);
+    sp = (long *)(s->vram_shadow + offset);
+    while ((n -= sizeof(*vp)) >= 0) {
+        if (*vp++ != *sp++) {
+            memcpy(sp - 1, vp - 1, n + sizeof(*vp));
+            return 1;
+        }
+    }
+    return 0;
+}
+
+#ifdef USE_SSE2
+
+#include <signal.h>
+#include <setjmp.h>
+#include <emmintrin.h>
+
+int sse2_ok = 1;
+
+static inline unsigned int cpuid_edx(unsigned int op)
+{
+    unsigned int eax, edx;
+
+    __asm__("cpuid"
+            : "=a" (eax), "=d" (edx)
+            : "0" (op)
+            : "bx", "cx");
+
+    return edx;
+}
+
+jmp_buf sse_jbuf;
+
+void intr(int sig)
+{
+    sse2_ok = 0;
+    longjmp(sse_jbuf, 1);
+}
+
+void check_sse2(void)
+{
+    /* Check 1: What does CPUID say? */
+    if ((cpuid_edx(1) & 0x4000000) == 0) {
+        sse2_ok = 0;
+        return;
+    }
+
+    /* Check 2: Can we use SSE2 in anger? */
+    signal(SIGILL, intr);
+    if (setjmp(sse_jbuf) == 0)
+        __asm__("xorps %xmm0,%xmm0\n");
+}
+
+int vram_dirty(VGAState *s, int offset, int n)
+{
+    __m128i *sp, *vp;
+
+    if (s->vram_shadow == NULL)
+        return 1;
+    if (sse2_ok == 0)
+        return cmp_vram(s, offset, n);
+    vp = (__m128i *)(s->vram_ptr + offset);
+    sp = (__m128i *)(s->vram_shadow + offset);
+    while ((n -= sizeof(*vp)) >= 0) {
+        if (_mm_movemask_epi8(_mm_cmpeq_epi8(*sp, *vp)) != 0xffff) {
+            while (n >= 0) {
+                _mm_store_si128(sp++, _mm_load_si128(vp++));
+                n -= sizeof(*vp);
+            }
+            return 1;
+        }
+        sp++;
+        vp++;
+    }
+    return 0;
+}
+#else /* !USE_SSE2 */
+int vram_dirty(VGAState *s, int offset, int n)
+{
+    return cmp_vram(s, offset, n);
+}
+
+void check_sse2(void)
+{
+}
+#endif /* !USE_SSE2 */
+
 /* 
  * graphic modes
  */
@@ -1434,6 +1527,9 @@ static void vga_draw_graphic(VGAState *s, int full_update)
     printf("w=%d h=%d v=%d line_offset=%d cr[0x09]=0x%02x cr[0x17]=0x%02x linecmp=%d sr[0x01]=0x%02x\n",
            width, height, v, line_offset, s->cr[9], s->cr[0x17], s->line_compare, s->sr[0x01]);
 #endif
+    for (y = 0; y < s->vram_size; y += TARGET_PAGE_SIZE)
+        if (vram_dirty(s, y, TARGET_PAGE_SIZE))
+            cpu_physical_memory_set_dirty(s->vram_offset + y);
     addr1 = (s->start_addr * 4);
     bwidth = width * 4;
     y_start = -1;
@@ -1536,9 +1632,18 @@ static void vga_draw_blank(VGAState *s, int full_update)
 
 void vga_update_display(void)
 {
+    static int loop;
     VGAState *s = vga_state;
     int full_update, graphic_mode;
 
+    /*
+     * Only update the display every other time.  The responsiveness is
+     * acceptable and it cuts down on the overhead of the VRAM compare
+     * in `vram_dirty'.
+     */
+    if (loop++ & 1)
+        return;
+
     if (s->ds->depth == 0) {
         /* nothing to do */
     } else {
@@ -1569,7 +1674,6 @@ void vga_update_display(void)
             full_update = 1;
         }
 
-        full_update = 1;
         switch(graphic_mode) {
         case GMODE_TEXT:
             vga_draw_text(s, full_update);
@@ -1874,7 +1978,13 @@ void vga_common_init(VGAState *s, DisplayState *ds, uint8_t *vga_ram_base,
 #else
     s->vram_ptr = qemu_malloc(vga_ram_size);
 #endif
-
+    check_sse2();
+    s->vram_shadow = qemu_malloc(vga_ram_size+TARGET_PAGE_SIZE+1);
+    if (s->vram_shadow == NULL)
+        fprintf(stderr, "Cannot allocate %d bytes for VRAM shadow, "
+                "mouse will be slow\n", vga_ram_size);
+    s->vram_shadow = (uint8_t *)((long)(s->vram_shadow + TARGET_PAGE_SIZE - 1)
+                                 & ~(TARGET_PAGE_SIZE - 1));
     s->vram_offset = vga_ram_offset;
     s->vram_size = vga_ram_size;
     s->ds = ds;

diff --git a/tools/ioemu/hw/vga_int.h b/tools/ioemu/hw/vga_int.h
index ca7ec373bc0930e802c6ad6161313eb4259f5e52..1789df51e6aa2bb0bf6e509592a38f6413555e6d 100644 (file)
--- a/tools/ioemu/hw/vga_int.h
+++ b/tools/ioemu/hw/vga_int.h
@@ -76,6 +76,7 @@
 
 #define VGA_STATE_COMMON                                                \
     uint8_t *vram_ptr;                                                  \
+    uint8_t *vram_shadow;                                               \
     unsigned long vram_offset;                                          \
     unsigned int vram_size;                                             \
     uint32_t latch;                                                     \

diff --git a/tools/ioemu/target-i386-dm/Makefile b/tools/ioemu/target-i386-dm/Makefile
index 887f73bea8fd4c50a3dcbb0ddd5f6f7e666b12ac..3219711167ff5139e3d2ebfa374b250658444376 100644 (file)
--- a/tools/ioemu/target-i386-dm/Makefile
+++ b/tools/ioemu/target-i386-dm/Makefile
@@ -13,8 +13,15 @@ ifdef CONFIG_USER_ONLY
 VPATH+=:$(SRC_PATH)/linux-user
 DEFINES+=-I$(SRC_PATH)/linux-user -I$(SRC_PATH)/linux-user/$(TARGET_ARCH)
 endif
-CFLAGS+=-g -fno-strict-aliasing
-LDFLAGS=-g
+
+SSE2 := $(call test-gcc-flag,$(CC),-msse2)
+ifeq ($(SSE2),-msse2)
+CFLAGS += -DUSE_SSE2=1 -msse2
+endif
+
+CFLAGS += -g -fno-strict-aliasing $(LOCAL_CFLAGS)
+LDFLAGS = -g
+
 LIBS=
 HELPER_CFLAGS=$(CFLAGS)
 DYNGEN=../dyngen$(EXESUF)