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memory: protect current_map by RCU 

Replace the flat_view_mutex with RCU, avoiding futex contention for
dataplane on large systems and many iothreads.

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2013-05-17 12:37:03 +02:00
parent b476c99d01
commit 374f2981d1
2 changed files with 28 additions and 31 deletions
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5
include/exec/memory.h
View File

@ -33,6 +33,7 @@
#include "qemu/notify.h"
#include "qapi/error.h"
#include "qom/object.h"
#include "qemu/rcu.h"
#define MAX_PHYS_ADDR_SPACE_BITS 62
#define MAX_PHYS_ADDR (((hwaddr)1 << MAX_PHYS_ADDR_SPACE_BITS) - 1)
@ -207,9 +208,13 @@ struct MemoryListener {
*/
struct AddressSpace {
/* All fields are private. */
struct rcu_head rcu;
char *name;
MemoryRegion *root;
/* Accessed via RCU. */
struct FlatView *current_map;
int ioeventfd_nb;
struct MemoryRegionIoeventfd *ioeventfds;
struct AddressSpaceDispatch *dispatch;

54
memory.c
View File

@ -33,26 +33,12 @@ static bool memory_region_update_pending;
static bool ioeventfd_update_pending;
static bool global_dirty_log = false;
/* flat_view_mutex is taken around reading as->current_map; the critical
* section is extremely short, so I'm using a single mutex for every AS.
* We could also RCU for the read-side.
*
* The BQL is taken around transaction commits, hence both locks are taken
* while writing to as->current_map (with the BQL taken outside).
*/
static QemuMutex flat_view_mutex;
static QTAILQ_HEAD(memory_listeners, MemoryListener) memory_listeners
= QTAILQ_HEAD_INITIALIZER(memory_listeners);
static QTAILQ_HEAD(, AddressSpace) address_spaces
= QTAILQ_HEAD_INITIALIZER(address_spaces);
static void memory_init(void)
{
qemu_mutex_init(&flat_view_mutex);
}
typedef struct AddrRange AddrRange;
/*
@ -242,6 +228,7 @@ struct FlatRange {
* order.
*/
struct FlatView {
struct rcu_head rcu;
unsigned ref;
FlatRange *ranges;
unsigned nr;
@ -654,10 +641,10 @@ static FlatView *address_space_get_flatview(AddressSpace *as)
{
FlatView *view;
qemu_mutex_lock(&flat_view_mutex);
view = as->current_map;
rcu_read_lock();
view = atomic_rcu_read(&as->current_map);
flatview_ref(view);
qemu_mutex_unlock(&flat_view_mutex);
rcu_read_unlock();
return view;
}
@ -766,10 +753,9 @@ static void address_space_update_topology(AddressSpace *as)
address_space_update_topology_pass(as, old_view, new_view, false);
address_space_update_topology_pass(as, old_view, new_view, true);
qemu_mutex_lock(&flat_view_mutex);
flatview_unref(as->current_map);
as->current_map = new_view;
qemu_mutex_unlock(&flat_view_mutex);
/* Writes are protected by the BQL. */
atomic_rcu_set(&as->current_map, new_view);
call_rcu(old_view, flatview_unref, rcu);
/* Note that all the old MemoryRegions are still alive up to this
* point. This relieves most MemoryListeners from the need to
@ -1957,10 +1943,6 @@ void memory_listener_unregister(MemoryListener *listener)
void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
{
if (QTAILQ_EMPTY(&address_spaces)) {
memory_init();
}
memory_region_transaction_begin();
as->root = root;
as->current_map = g_new(FlatView, 1);
@ -1974,15 +1956,10 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
memory_region_transaction_commit();
}
void address_space_destroy(AddressSpace *as)
static void do_address_space_destroy(AddressSpace *as)
{
MemoryListener *listener;
/* Flush out anything from MemoryListeners listening in on this */
memory_region_transaction_begin();
as->root = NULL;
memory_region_transaction_commit();
QTAILQ_REMOVE(&address_spaces, as, address_spaces_link);
address_space_destroy_dispatch(as);
QTAILQ_FOREACH(listener, &memory_listeners, link) {
@ -1994,6 +1971,21 @@ void address_space_destroy(AddressSpace *as)
g_free(as->ioeventfds);
}
void address_space_destroy(AddressSpace *as)
{
/* Flush out anything from MemoryListeners listening in on this */
memory_region_transaction_begin();
as->root = NULL;
memory_region_transaction_commit();
QTAILQ_REMOVE(&address_spaces, as, address_spaces_link);
/* At this point, as->dispatch and as->current_map are dummy
* entries that the guest should never use. Wait for the old
* values to expire before freeing the data.
*/
call_rcu(as, do_address_space_destroy, rcu);
}
bool io_mem_read(MemoryRegion *mr, hwaddr addr, uint64_t *pval, unsigned size)
{
return memory_region_dispatch_read(mr, addr, pval, size);