qemu-kvm/SOURCES/kvm-multifd-Only-flush-once-each-full-round-of-memory.patch

From e6f770506091eada46c63ac1c8b934b508e3807f Mon Sep 17 00:00:00 2001
From: Juan Quintela <quintela@redhat.com>
Date: Tue, 21 Jun 2022 13:36:11 +0200
Subject: [PATCH 07/12] multifd: Only flush once each full round of memory
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RH-Author: quintela1 <quintela@redhat.com>
RH-MergeRequest: 186: Multifd flushes its channels 10 times per second
RH-Bugzilla: 2196295
RH-Acked-by: Peter Xu <peterx@redhat.com>
RH-Acked-by: Leonardo Brás <leobras@redhat.com>
RH-Commit: [3/3] 33f76dfc72a2552a42dc7f0fe3923564185a7bf7 (juan.quintela/c9s-qemu-kvm)

We need to add a new flag to mean to flush at that point.
Notice that we still flush at the end of setup and at the end of
complete stages.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>

---

Add missing qemu_fflush(), now it passes all tests always.
In the previous version, the check that changes the default value to
false got lost in some rebase.  Get it back.

(cherry picked from commit 294e5a4034e81b3d8db03b4e0f691386f20d6ed3)
---
 migration/migration.h |  3 +--
 migration/options.c   |  8 ++------
 migration/ram.c       | 28 +++++++++++++++++++++++++++-
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/migration/migration.h b/migration/migration.h
index 04c78c1fd6..dfec649af8 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -419,8 +419,7 @@ struct MigrationState {
      * 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 property has no effect
-     * until the patch that removes this comment.  (since 8.1)
+     * Default value is false. (since 8.1)
      */
     bool multifd_flush_after_each_section;
     /*
diff --git a/migration/options.c b/migration/options.c
index 5b0d080ecb..e13c7cb8e5 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -89,7 +89,7 @@ Property migration_properties[] = {
     DEFINE_PROP_BOOL("decompress-error-check", MigrationState,
                       decompress_error_check, true),
     DEFINE_PROP_BOOL("multifd-flush-after-each-section", MigrationState,
-                      multifd_flush_after_each_section, true),
+                      multifd_flush_after_each_section, false),
     DEFINE_PROP_UINT8("x-clear-bitmap-shift", MigrationState,
                       clear_bitmap_shift, CLEAR_BITMAP_SHIFT_DEFAULT),
     DEFINE_PROP_BOOL("x-preempt-pre-7-2", MigrationState,
@@ -350,11 +350,7 @@ 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 property is enabled.
-     */
-    return true || s->multifd_flush_after_each_section;
+    return s->multifd_flush_after_each_section;
 }
 
 bool migrate_postcopy(void)
diff --git a/migration/ram.c b/migration/ram.c
index 1e2414d681..e9dcda8b9d 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -86,6 +86,7 @@
 #define RAM_SAVE_FLAG_XBZRLE   0x40
 /* 0x80 is reserved in qemu-file.h for RAM_SAVE_FLAG_HOOK */
 #define RAM_SAVE_FLAG_COMPRESS_PAGE    0x100
+#define RAM_SAVE_FLAG_MULTIFD_FLUSH    0x200
 /* We can't use any flag that is bigger than 0x200 */
 
 int (*xbzrle_encode_buffer_func)(uint8_t *, uint8_t *, int,
@@ -1581,6 +1582,7 @@ retry:
  * associated with the search process.
  *
  * Returns:
+ *         <0: An error happened
  *         PAGE_ALL_CLEAN: no dirty page found, give up
  *         PAGE_TRY_AGAIN: no dirty page found, retry for next block
  *         PAGE_DIRTY_FOUND: dirty page found
@@ -1608,6 +1610,15 @@ static int find_dirty_block(RAMState *rs, PageSearchStatus *pss)
         pss->page = 0;
         pss->block = QLIST_NEXT_RCU(pss->block, next);
         if (!pss->block) {
+            if (!migrate_multifd_flush_after_each_section()) {
+                QEMUFile *f = rs->pss[RAM_CHANNEL_PRECOPY].pss_channel;
+                int ret = multifd_send_sync_main(f);
+                if (ret < 0) {
+                    return ret;
+                }
+                qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
+                qemu_fflush(f);
+            }
             /*
              * If memory migration starts over, we will meet a dirtied page
              * which may still exists in compression threads's ring, so we
@@ -2600,6 +2611,9 @@ static int ram_find_and_save_block(RAMState *rs)
                     break;
                 } else if (res == PAGE_TRY_AGAIN) {
                     continue;
+                } else if (res < 0) {
+                    pages = res;
+                    break;
                 }
             }
         }
@@ -3286,6 +3300,10 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
         return ret;
     }
 
+    if (!migrate_multifd_flush_after_each_section()) {
+        qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
+    }
+
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
     qemu_fflush(f);
 
@@ -3471,6 +3489,9 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
         return ret;
     }
 
+    if (!migrate_multifd_flush_after_each_section()) {
+        qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
+    }
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
     qemu_fflush(f);
 
@@ -4152,7 +4173,9 @@ int ram_load_postcopy(QEMUFile *f, int channel)
             }
             decompress_data_with_multi_threads(f, page_buffer, len);
             break;
-
+        case RAM_SAVE_FLAG_MULTIFD_FLUSH:
+            multifd_recv_sync_main();
+            break;
         case RAM_SAVE_FLAG_EOS:
             /* normal exit */
             if (migrate_multifd_flush_after_each_section()) {
@@ -4426,6 +4449,9 @@ static int ram_load_precopy(QEMUFile *f)
                 break;
             }
             break;
+        case RAM_SAVE_FLAG_MULTIFD_FLUSH:
+            multifd_recv_sync_main();
+            break;
         case RAM_SAVE_FLAG_EOS:
             /* normal exit */
             if (migrate_multifd_flush_after_each_section()) {
-- 
2.39.3