[PATCH v6 1/3] multifd: Create property multifd-flush-after-each-section

[Juan Quintela]

We used to flush all channels at the end of each RAM section
sent.  That is not needed, so preparing to only flush after a full
iteration through all the RAM.

Default value of the property is false.  But we return "true" in
migrate_multifd_flush_after_each_section() until we implement the code
in following patches.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

---

Rename each-iteration to after-each-section
Rename multifd-sync-after-each-section to
       multifd-flush-after-each-section
---
 qapi/migration.json   | 21 ++++++++++++++++++++-
 migration/migration.h |  1 +
 hw/core/machine.c     |  1 +
 migration/migration.c | 17 +++++++++++++++--
 4 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index c84fa10e86..3afd81174d 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -478,6 +478,24 @@
 #                    should not affect the correctness of postcopy migration.
 #                    (since 7.1)
 #
+# @multifd-flush-after-each-section: flush every channel after each
+#                                    section sent.  This assures that
+#                                    we can't mix pages from one
+#                                    iteration through ram pages with
+#                                    pages for the following
+#                                    iteration.  We really only need
+#                                    to do this flush after we have go
+#                                    through all the dirty pages.
+#                                    For historical reasons, we do
+#                                    that after each section.  This is
+#                                    suboptimal (we flush too many
+#                                    times).
+#                                    Default value is false.
+#                                    Setting this capability has no
+#                                    effect until the patch that
+#                                    removes this comment.
+#                                    (since 8.0)
+#
 # Features:
 # @unstable: Members @x-colo and @x-ignore-shared are experimental.
 #
@@ -492,7 +510,8 @@
            'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
            { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
            'validate-uuid', 'background-snapshot',
-           'zero-copy-send', 'postcopy-preempt'] }
+           'zero-copy-send', 'postcopy-preempt',
+           'multifd-flush-after-each-section'] }
 
 ##
 # @MigrationCapabilityStatus:
diff --git a/migration/migration.h b/migration/migration.h
index 2da2f8a164..7f0f4260ba 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -424,6 +424,7 @@ int migrate_multifd_channels(void);
 MultiFDCompression migrate_multifd_compression(void);
 int migrate_multifd_zlib_level(void);
 int migrate_multifd_zstd_level(void);
+bool migrate_multifd_flush_after_each_section(void);
 
 #ifdef CONFIG_LINUX
 bool migrate_use_zero_copy_send(void);
diff --git a/hw/core/machine.c b/hw/core/machine.c
index f73fc4c45c..602e775f34 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -54,6 +54,7 @@ const size_t hw_compat_7_1_len = G_N_ELEMENTS(hw_compat_7_1);
 GlobalProperty hw_compat_7_0[] = {
     { "arm-gicv3-common", "force-8-bit-prio", "on" },
     { "nvme-ns", "eui64-default", "on"},
+    { "migration", "multifd-flush-after-each-section", "on"},
 };
 const size_t hw_compat_7_0_len = G_N_ELEMENTS(hw_compat_7_0);
 
diff --git a/migration/migration.c b/migration/migration.c
index 90fca70cb7..cfba0da005 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -167,7 +167,8 @@ INITIALIZE_MIGRATE_CAPS_SET(check_caps_background_snapshot,
     MIGRATION_CAPABILITY_XBZRLE,
     MIGRATION_CAPABILITY_X_COLO,
     MIGRATION_CAPABILITY_VALIDATE_UUID,
-    MIGRATION_CAPABILITY_ZERO_COPY_SEND);
+    MIGRATION_CAPABILITY_ZERO_COPY_SEND,
+    MIGRATION_CAPABILITY_MULTIFD_FLUSH_AFTER_EACH_SECTION);
 
 /* When we add fault tolerance, we could have several
    migrations at once.  For now we don't need to add
@@ -2701,6 +2702,17 @@ bool migrate_use_multifd(void)
     return s->enabled_capabilities[MIGRATION_CAPABILITY_MULTIFD];
 }
 
+bool migrate_multifd_flush_after_each_section(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    /*
+     * Until the patch that remove this comment, we always return that
+     * the capability is enabled.
+     */
+    return true || 
s->enabled_capabilities[MIGRATION_CAPABILITY_MULTIFD_FLUSH_AFTER_EACH_SECTION];
+}
+
 bool migrate_pause_before_switchover(void)
 {
     MigrationState *s;
@@ -4535,7 +4547,8 @@ static Property migration_properties[] = {
     DEFINE_PROP_MIG_CAP("x-zero-copy-send",
             MIGRATION_CAPABILITY_ZERO_COPY_SEND),
 #endif
-
+    DEFINE_PROP_MIG_CAP("multifd-flush-after-each-section",
+                        MIGRATION_CAPABILITY_MULTIFD_FLUSH_AFTER_EACH_SECTION),
     DEFINE_PROP_END_OF_LIST(),
 };
 
-- 
2.39.1