commit a0c78d815c34e81feedae60347734d28b1098a27
author Fabiano Rosas <farosas@suse.de> Tue Aug 27 14:46:00 2024 -0300
committer Fabiano Rosas <farosas@suse.de> Tue Sep 03 16:24:36 2024 -0300
tree 69da0a7db9dba82fe711eee21a00795d551cf164
parent a71ef5c7f329533a49ab164b92945267be864ede

migration/multifd: Allow multifd sync without flush

Separate the multifd sync from flushing the client data to the
channels. These two operations are closely related but not strictly
necessary to be executed together.

The multifd sync is intrinsic to how multifd works. The multiple
channels operate independently and may finish IO out of order in
relation to each other. This applies also between the source and
destination QEMU.

Flushing the data that is left in the client-owned data structures
(e.g. MultiFDPages_t) prior to sync is usually the right thing to do,
but that is particular to how the ram migration is implemented with
several passes over dirty data.

Make these two routines separate, allowing future code to call the
sync by itself if needed. This also allows the usage of
multifd_ram_send to be isolated to ram code.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>

migration/multifd.c

diff --git a/migration/multifd.c b/migration/multifd.c
index cb7a121..ce08257 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -914,11 +914,8 @@
     return ret;
 }
 
-int multifd_send_sync_main(void)
+int multifd_ram_flush_and_sync(void)
 {
-    int i;
-    bool flush_zero_copy;
-
     if (!migrate_multifd()) {
         return 0;
     }
@@ -930,6 +927,14 @@
         }
     }
 
+    return multifd_send_sync_main();
+}
+
+int multifd_send_sync_main(void)
+{
+    int i;
+    bool flush_zero_copy;
+
     flush_zero_copy = migrate_zero_copy_send();
 
     for (i = 0; i < migrate_multifd_channels(); i++) {

migration/multifd.h

diff --git a/migration/multifd.h b/migration/multifd.h
index 5fa384d..00c872d 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -270,4 +270,5 @@
 
 void multifd_ram_save_setup(void);
 void multifd_ram_save_cleanup(void);
+int multifd_ram_flush_and_sync(void);
 #endif

migration/ram.c

diff --git a/migration/ram.c b/migration/ram.c
index 1815b25..67ca3d5 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1326,7 +1326,7 @@
                 (!migrate_multifd_flush_after_each_section() ||
                  migrate_mapped_ram())) {
                 QEMUFile *f = rs->pss[RAM_CHANNEL_PRECOPY].pss_channel;
-                int ret = multifd_send_sync_main();
+                int ret = multifd_ram_flush_and_sync();
                 if (ret < 0) {
                     return ret;
                 }
@@ -3066,7 +3066,7 @@
     }
 
     bql_unlock();
-    ret = multifd_send_sync_main();
+    ret = multifd_ram_flush_and_sync();
     bql_lock();
     if (ret < 0) {
         error_setg(errp, "%s: multifd synchronization failed", __func__);
@@ -3213,7 +3213,7 @@
         && migration_is_setup_or_active()) {
         if (migrate_multifd() && migrate_multifd_flush_after_each_section() &&
             !migrate_mapped_ram()) {
-            ret = multifd_send_sync_main();
+            ret = multifd_ram_flush_and_sync();
             if (ret < 0) {
                 return ret;
             }
@@ -3285,7 +3285,7 @@
         }
     }
 
-    ret = multifd_send_sync_main();
+    ret = multifd_ram_flush_and_sync();
     if (ret < 0) {
         return ret;
     }