[Qemu-devel] [PATCH 13/13] migration: flush receive queue

[Juan Quintela]

From: Juan Quintela <address@hidden>

Each time that we sync the bitmap, it is a possiblity that we receive
a page that is being processed by a different thread.  We fix this
problem just making sure that we wait for all receiving threads to
finish its work before we procedeed with the next stage.

I tried to make a migration command for it, but it don't work because
we sync the bitmap sometimes when we have already sent the beggining
of the section, so I just added a new page flag.

Signed-off-by: Juan Quintela <address@hidden>
---
 include/migration/migration.h |  1 +
 migration/ram.c               | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index afdc7ec..49e2ec6 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -251,6 +251,7 @@ void migrate_multifd_send_threads_create(void);
 void migrate_multifd_send_threads_join(void);
 void migrate_multifd_recv_threads_create(void);
 void migrate_multifd_recv_threads_join(void);
+void qemu_savevm_send_multifd_flush(QEMUFile *f);

 void migrate_compress_threads_create(void);
 void migrate_compress_threads_join(void);
diff --git a/migration/ram.c b/migration/ram.c
index 9a20f63..bf2022e 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -69,6 +69,7 @@ static uint64_t bitmap_sync_count;
 /* 0x80 is reserved in migration.h start with 0x100 next */
 #define RAM_SAVE_FLAG_COMPRESS_PAGE    0x100
 #define RAM_SAVE_FLAG_MULTIFD_PAGE     0x200
+#define RAM_SAVE_FLAG_MULTIFD_FLUSH    0x400

 static const uint8_t ZERO_TARGET_PAGE[TARGET_PAGE_SIZE];

@@ -398,6 +399,11 @@ void migrate_compress_threads_create(void)

 /* Multiple fd's */

+
+/* Indicates if we have synced the bitmap and we need to assure that
+   target has processeed all previous pages */
+bool multifd_needs_flush = false;
+
 struct MultiFDSendParams {
     /* not changed */
     QemuThread thread;
@@ -713,6 +719,25 @@ static void multifd_recv_page(uint8_t *address, int fd_num)
     qemu_mutex_unlock(&params->mutex);
 }

+
+static int multifd_flush(void)
+{
+    int i, thread_count;
+
+    if (!migrate_multifd()) {
+        return 0;
+    }
+    thread_count = migrate_multifd_threads();
+    qemu_mutex_lock(&multifd_recv_mutex);
+    for (i = 0; i < thread_count; i++) {
+        while(!multifd_recv[i].done) {
+            qemu_cond_wait(&multifd_recv_cond, &multifd_recv_mutex);
+        }
+    }
+    qemu_mutex_unlock(&multifd_recv_mutex);
+    return 0;
+}
+
 /**
  * save_page_header: Write page header to wire
  *
@@ -729,6 +754,11 @@ static size_t save_page_header(QEMUFile *f, RAMBlock 
*block, ram_addr_t offset)
 {
     size_t size, len;

+    if (multifd_needs_flush) {
+        offset |= RAM_SAVE_FLAG_MULTIFD_FLUSH;
+        multifd_needs_flush = false;
+    }
+
     qemu_put_be64(f, offset);
     size = 8;

@@ -2399,6 +2429,9 @@ static int ram_save_complete(QEMUFile *f, void *opaque)

     if (!migration_in_postcopy(migrate_get_current())) {
         migration_bitmap_sync();
+        if (migrate_multifd()) {
+            multifd_needs_flush = true;
+        }
     }

     ram_control_before_iterate(f, RAM_CONTROL_FINISH);
@@ -2440,6 +2473,9 @@ static void ram_save_pending(QEMUFile *f, void *opaque, 
uint64_t max_size,
         qemu_mutex_lock_iothread();
         rcu_read_lock();
         migration_bitmap_sync();
+        if (migrate_multifd()) {
+            multifd_needs_flush = true;
+        }
         rcu_read_unlock();
         qemu_mutex_unlock_iothread();
         remaining_size = ram_save_remaining() * TARGET_PAGE_SIZE;
@@ -2851,6 +2887,10 @@ static int ram_load(QEMUFile *f, void *opaque, int 
version_id)
         flags = addr & ~TARGET_PAGE_MASK;
         addr &= TARGET_PAGE_MASK;

+        if (flags & RAM_SAVE_FLAG_MULTIFD_FLUSH) {
+            multifd_flush();
+            flags = flags & (~RAM_SAVE_FLAG_MULTIFD_FLUSH);
+        }
         if (flags & (RAM_SAVE_FLAG_COMPRESS | RAM_SAVE_FLAG_PAGE |
                      RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE |
                      RAM_SAVE_FLAG_MULTIFD_PAGE)) {
-- 
2.7.4