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[Qemu-devel] [PATCH 4/8] memory: avoid unnecessary object_ref/unref
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 4/8] memory: avoid unnecessary object_ref/unref |
Date: |
Wed, 16 Dec 2015 11:59:56 +0100 |
For the common case of DMA into non-hotplugged RAM, it is unnecessary
but expensive to do object_ref/unref. Add back an owner field to
MemoryRegion, so that these memory regions can skip the reference
counting.
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/exec/memory.h | 1 +
memory.c | 28 ++++++++++++----------------
2 files changed, 13 insertions(+), 16 deletions(-)
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 5b1fd12..24b7cba 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -172,6 +172,7 @@ struct MemoryRegion {
bool global_locking;
uint8_t dirty_log_mask;
ram_addr_t ram_addr;
+ Object *owner;
const MemoryRegionIOMMUOps *iommu_ops;
const MemoryRegionOps *ops;
diff --git a/memory.c b/memory.c
index c0770a6..1783300 100644
--- a/memory.c
+++ b/memory.c
@@ -908,20 +908,22 @@ void memory_region_init(MemoryRegion *mr,
const char *name,
uint64_t size)
{
- if (!owner) {
- owner = container_get(qdev_get_machine(), "/unattached");
- }
-
object_initialize(mr, sizeof(*mr), TYPE_MEMORY_REGION);
mr->size = int128_make64(size);
if (size == UINT64_MAX) {
mr->size = int128_2_64();
}
mr->name = g_strdup(name);
+ mr->owner = owner;
if (name) {
char *escaped_name = memory_region_escape_name(name);
char *name_array = g_strdup_printf("%s[*]", escaped_name);
+
+ if (!owner) {
+ owner = container_get(qdev_get_machine(), "/unattached");
+ }
+
object_property_add_child(owner, name_array, OBJECT(mr), &error_abort);
object_unref(OBJECT(mr));
g_free(name_array);
@@ -1341,24 +1343,18 @@ void memory_region_ref(MemoryRegion *mr)
* The memory region is a child of its owner. As long as the
* owner doesn't call unparent itself on the memory region,
* ref-ing the owner will also keep the memory region alive.
- * Memory regions without an owner are supposed to never go away,
- * but we still ref/unref them for debugging purposes.
+ * Memory regions without an owner are supposed to never go away;
+ * we do not ref/unref them because it slows down DMA sensibly.
*/
- Object *obj = OBJECT(mr);
- if (obj && obj->parent) {
- object_ref(obj->parent);
- } else {
- object_ref(obj);
+ if (mr && mr->owner) {
+ object_ref(mr->owner);
}
}
void memory_region_unref(MemoryRegion *mr)
{
- Object *obj = OBJECT(mr);
- if (obj && obj->parent) {
- object_unref(obj->parent);
- } else {
- object_unref(obj);
+ if (mr && mr->owner) {
+ object_unref(mr->owner);
}
}
--
2.5.0
- [Qemu-devel] [PATCH 0/8] Optimize address_space_read/write/map, Paolo Bonzini, 2015/12/16
- [Qemu-devel] [PATCH 3/8] memory: reorder MemoryRegion fields, Paolo Bonzini, 2015/12/16
- [Qemu-devel] [PATCH 5/8] memory: split address_space_read and address_space_write, Paolo Bonzini, 2015/12/16
- [Qemu-devel] [PATCH 1/8] exec: always call qemu_get_ram_ptr within rcu_read_lock, Paolo Bonzini, 2015/12/16
- [Qemu-devel] [PATCH 4/8] memory: avoid unnecessary object_ref/unref,
Paolo Bonzini <=
- [Qemu-devel] [PATCH 2/8] exec: make qemu_ram_ptr_length more similar to qemu_get_ram_ptr, Paolo Bonzini, 2015/12/16
- [Qemu-devel] [PATCH 8/8] memory: try to inline constant-length reads, Paolo Bonzini, 2015/12/16
- [Qemu-devel] [PATCH 6/8] memory: extract first iteration of address_space_read and address_space_write, Paolo Bonzini, 2015/12/16
- [Qemu-devel] [PATCH] memory: try to inline constant-length reads, Paolo Bonzini, 2015/12/16
- [Qemu-devel] [PATCH 7/8] memory: inline a few small accessors, Paolo Bonzini, 2015/12/16