[Qemu-devel] [PATCH 2/4] memory: streamline common case for memory dispatch

[Paolo Bonzini]

In the common case where there is no combining or splitting,
access_with_adjusted_size is adding a lot of overhead.  Call
the MMIO ops directly in that case.

Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
 memory.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 56 insertions(+), 12 deletions(-)

diff --git a/memory.c b/memory.c
index 56e54aa..1ade19c 100644
--- a/memory.c
+++ b/memory.c
@@ -443,6 +443,7 @@ static void memory_region_write_accessor(MemoryRegion *mr,
 static void access_with_adjusted_size(hwaddr addr,
                                       uint64_t *value,
                                       unsigned size,
+                                      unsigned access_size,
                                       void (*access)(MemoryRegion *mr,
                                                      hwaddr addr,
                                                      uint64_t *value,
@@ -452,11 +453,9 @@ static void access_with_adjusted_size(hwaddr addr,
                                       MemoryRegion *mr)
 {
     uint64_t access_mask;
-    unsigned access_size;
     unsigned i;
 
     /* FIXME: support unaligned access? */
-    access_size = MAX(MIN(size, mr->min_access_size), mr->min_access_size);
     access_mask = -1ULL >> (64 - access_size * 8);
     if (memory_region_big_endian(mr)) {
         for (i = 0; i < size; i += access_size) {
@@ -929,13 +928,32 @@ static uint64_t memory_region_dispatch_read1(MemoryRegion 
*mr,
                                              hwaddr addr,
                                              unsigned size)
 {
+    unsigned access_size;
     uint64_t data = 0;
 
+    if (size < mr->min_access_size) {
+        access_size = mr->min_access_size;
+        goto adjusted;
+    }
+    if (size > mr->max_access_size) {
+        access_size = mr->max_access_size;
+        goto adjusted;
+    }
+
+    if (mr->ops->read) {
+        data = mr->ops->read(mr->opaque, addr, size);
+    } else {
+        data = mr->ops->old_mmio.read[ctz32(size)](mr->opaque, addr);
+    }
+    trace_memory_region_ops_read(mr, addr, data, size);
+    return data;
+
+adjusted:
     if (mr->ops->read) {
-        access_with_adjusted_size(addr, &data, size,
+        access_with_adjusted_size(addr, &data, size, access_size,
                                   memory_region_read_accessor, mr);
     } else {
-        access_with_adjusted_size(addr, &data, size,
+        access_with_adjusted_size(addr, &data, size, access_size,
                                   memory_region_oldmmio_read_accessor, mr);
     }
 
@@ -957,6 +975,39 @@ static bool memory_region_dispatch_read(MemoryRegion *mr,
     return false;
 }
 
+static void memory_region_dispatch_write1(MemoryRegion *mr,
+                                          hwaddr addr,
+                                          uint64_t data,
+                                          unsigned size)
+{
+    unsigned access_size;
+    if (size < mr->min_access_size) {
+        access_size = mr->min_access_size;
+        goto adjusted;
+    }
+    if (size > mr->max_access_size) {
+        access_size = mr->max_access_size;
+        goto adjusted;
+    }
+
+    trace_memory_region_ops_write(mr, addr, data, size);
+    if (mr->ops->write) {
+        mr->ops->write(mr->opaque, addr, data, size);
+    } else {
+        mr->ops->old_mmio.write[ctz32(size)](mr->opaque, addr, data);
+    }
+    return;
+
+adjusted:
+    if (mr->ops->write) {
+        access_with_adjusted_size(addr, &data, size, access_size,
+                                  memory_region_write_accessor, mr);
+    } else {
+        access_with_adjusted_size(addr, &data, size, access_size,
+                                  memory_region_oldmmio_write_accessor, mr);
+    }
+}
+
 static bool memory_region_dispatch_write(MemoryRegion *mr,
                                          hwaddr addr,
                                          uint64_t data,
@@ -968,14 +1019,7 @@ static bool memory_region_dispatch_write(MemoryRegion *mr,
     }
 
     adjust_endianness(mr, &data, size);
-
-    if (mr->ops->write) {
-        access_with_adjusted_size(addr, &data, size,
-                                  memory_region_write_accessor, mr);
-    } else {
-        access_with_adjusted_size(addr, &data, size,
-                                  memory_region_oldmmio_write_accessor, mr);
-    }
+    memory_region_dispatch_write1(mr, addr, data, size);
     return false;
 }
 
-- 
1.8.4.2