[RFC PATCH v2 2/3] fine grained qemu_mutex locking for migration

Umesh Deshpande
2011-07-29T20:57:34Z

In the migration thread, qemu_mutex is released during the most time consuming
part. i.e. during is_dup_page which identifies the uniform data pages and during
the put_buffer. qemu_mutex is also released while blocking on select to wait for
the descriptor to become ready for writes.

Signed-off-by: Umesh Deshpande <udeshpan@redhat.com>
---
arch_init.c | 14 +++++++++++---
migration.c | 11 +++++++----
2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/arch_init.c b/arch_init.c
index 484b39d..cd545bc 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -110,7 +110,7 @@ static int is_dup_page(uint8_t *page, uint8_t ch)
static RAMBlock *last_block;
static ram_addr_t last_offset;

-static int ram_save_block(QEMUFile *f)
+static int ram_save_block(QEMUFile *f, int stage)
{
RAMBlock *block = last_block;
ram_addr_t offset = last_offset;
@@ -131,6 +131,10 @@ static int ram_save_block(QEMUFile *f)
current_addr + TARGET_PAGE_SIZE,
MIGRATION_DIRTY_FLAG);

+ if (stage != 3) {
+ qemu_mutex_unlock_iothread();
+ }
+
p = block->host + offset;

if (is_dup_page(p, *p)) {
@@ -153,6 +157,10 @@ static int ram_save_block(QEMUFile *f)
bytes_sent = TARGET_PAGE_SIZE;
}

+ if (stage != 3) {
+ qemu_mutex_lock_iothread();
+ }
+
break;
}

@@ -301,7 +309,7 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, void *opaque)
while (!qemu_file_rate_limit(f)) {
int bytes_sent;

- bytes_sent = ram_save_block(f);
+ bytes_sent = ram_save_block(f, stage);
bytes_transferred += bytes_sent;
if (bytes_sent == 0) { /* no more blocks */
break;
@@ -322,7 +330,7 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, void *opaque)
int bytes_sent;

/* flush all remaining blocks regardless of rate limiting */
- while ((bytes_sent = ram_save_block(f)) != 0) {
+ while ((bytes_sent = ram_save_block(f, stage)) != 0) {
bytes_transferred += bytes_sent;
}
cpu_physical_memory_set_dirty_tracking(0);
diff --git a/migration.c b/migration.c
index bf86067..992fef5 100644
--- a/migration.c
+++ b/migration.c
@@ -375,15 +375,19 @@ void migrate_fd_begin(void *arg)
if (ret < 0) {
DPRINTF("failed, %d\n", ret);
migrate_fd_error(s);
- goto out;
+ qemu_mutex_unlock_iothread();
+ return;
}

expire_time = qemu_get_clock_ms(rt_clock) + 100;
migrate_fd_put_ready(s);
+ qemu_mutex_unlock_iothread();

while (s->state == MIG_STATE_ACTIVE) {
if (migrate_fd_check_expire()) {
+ qemu_mutex_lock_iothread();
buffered_rate_tick(s->file);
+ qemu_mutex_unlock_iothread();
}

if (s->state != MIG_STATE_ACTIVE) {
@@ -392,12 +396,11 @@ void migrate_fd_begin(void *arg)

if (s->callback) {
migrate_fd_wait_for_unfreeze(s);
+ qemu_mutex_lock_iothread();
s->callback(s);
+ qemu_mutex_unlock_iothread();
}
}
-
-out:
- qemu_mutex_unlock_iothread();
}

--
1.7.4.1