multifd: Add COLO support

Like in the normal ram_load() path, put the received pages into the
colo cache and mark the pages in the bitmap so that they will be
flushed to the guest later.

Multifd with COLO is useful to reduce the VM pause time during checkpointing
for latency sensitive workloads. In such workloads the worst-case latency
is especially important.

Also, this is already worth it for the precopy phase as it helps with
converging. Moreover, multifd migration is the preferred way to do migration
nowadays and this allows to use multifd compression with COLO.

Benchmark:
Cluster nodes
 - Intel Xenon E5-2630 v3
 - 48Gb RAM
 - 10G Ethernet
Guest
 - Windows Server 2016
 - 6Gb RAM
 - 4 cores
Workload
 - Upload a file to the guest with SMB to simulate moderate
   memory dirtying
 - Measure the memory transfer time portion of each checkpoint
 - 600ms COLO checkpoint interval

Results
Plain
 idle mean: 4.50ms 99per: 10.33ms
 load mean: 24.30ms 99per: 78.05ms
Multifd-4
 idle mean: 6.48ms 99per: 10.41ms
 load mean: 14.12ms 99per: 31.27ms

Evaluation
While multifd has slightly higher latency when the guest idles, it is
10ms faster under load and more importantly it's worst case latency is
less than 1/2 of plain under load as can be seen in the 99. Percentile.

Co-authored-by: Juan Quintela <quintela@redhat.com>
[farosas: changed SoB to coauthored as Juan doesn't own that email address anymore]
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Link: https://lore.kernel.org/qemu-devel/20260302-colo_unit_test_multifd-v11-8-d653fb3b1d80@web.de
[removed license boilerplate]
Signed-off-by: Fabiano Rosas <farosas@suse.de>

diff --git a/MAINTAINERS b/MAINTAINERS
index df788658096510aa64f8ddb70ad9ceba7f134083..d8dc4c8d7b2cb38c371b55cd3ee0e7acc79e4258 100644 (file)
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3883,6 +3883,7 @@ COLO Framework
 M: Lukas Straub <lukasstraub2@web.de>
 S: Maintained
 F: migration/colo*
+F: migration/multifd-colo.*
 F: include/migration/colo.h
 F: include/migration/failover.h
 F: docs/COLO-FT.txt

diff --git a/migration/meson.build b/migration/meson.build
index c7f39bdb55239ecb0e775c77b90a1aa9e6a4a9ce..c9f0f5f9f2137536497e53e960ce70654ad1b394 100644 (file)
--- a/migration/meson.build
+++ b/migration/meson.build
@@ -39,7 +39,7 @@ system_ss.add(files(
 ), gnutls, zlib)
 
 if get_option('replication').allowed()
-  system_ss.add(files('colo-failover.c', 'colo.c'))
+  system_ss.add(files('colo-failover.c', 'colo.c', 'multifd-colo.c'))
 else
   system_ss.add(files('colo-stubs.c'))
 endif

diff --git a/migration/multifd-colo.c b/migration/multifd-colo.c
new file mode 100644 (file)
index 0000000..fb13e38
--- /dev/null
+++ b/migration/multifd-colo.c
@@ -0,0 +1,41 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * multifd colo implementation
+ *
+ * Copyright (c) Lukas Straub <lukasstraub2@web.de>
+ */
+
+#include "qemu/osdep.h"
+#include "multifd.h"
+#include "multifd-colo.h"
+#include "migration/colo.h"
+#include "system/ramblock.h"
+
+void multifd_colo_prepare_recv(MultiFDRecvParams *p)
+{
+    /*
+     * While we're still in precopy state (not yet in colo state), we copy
+     * received pages to both guest and cache. No need to set dirty bits,
+     * since guest and cache memory are in sync.
+     */
+    if (migration_incoming_in_colo_state()) {
+        colo_record_bitmap(p->block, p->normal, p->normal_num);
+        colo_record_bitmap(p->block, p->zero, p->zero_num);
+    }
+}
+
+void multifd_colo_process_recv(MultiFDRecvParams *p)
+{
+    if (!migration_incoming_in_colo_state()) {
+        for (int i = 0; i < p->normal_num; i++) {
+            void *guest = p->block->host + p->normal[i];
+            void *cache = p->host + p->normal[i];
+            memcpy(guest, cache, multifd_ram_page_size());
+        }
+        for (int i = 0; i < p->zero_num; i++) {
+            void *guest = p->block->host + p->zero[i];
+            memset(guest, 0, multifd_ram_page_size());
+        }
+    }
+}

diff --git a/migration/multifd-colo.h b/migration/multifd-colo.h
new file mode 100644 (file)
index 0000000..1011c5a
--- /dev/null
+++ b/migration/multifd-colo.h
@@ -0,0 +1,23 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * multifd colo header
+ *
+ * Copyright (c) Lukas Straub <lukasstraub2@web.de>
+ */
+
+#ifndef QEMU_MIGRATION_MULTIFD_COLO_H
+#define QEMU_MIGRATION_MULTIFD_COLO_H
+
+#ifdef CONFIG_REPLICATION
+
+void multifd_colo_prepare_recv(MultiFDRecvParams *p);
+void multifd_colo_process_recv(MultiFDRecvParams *p);
+
+#else
+
+static inline void multifd_colo_prepare_recv(MultiFDRecvParams *p) {}
+static inline void multifd_colo_process_recv(MultiFDRecvParams *p) {}
+
+#endif
+#endif

diff --git a/migration/multifd-nocomp.c b/migration/multifd-nocomp.c
index 9be79b3b8e00371ebff9e112766c225bec260bf7..9f7a792fa761b3bc30b971b35f464103a61787f0 100644 (file)
--- a/migration/multifd-nocomp.c
+++ b/migration/multifd-nocomp.c
@@ -16,6 +16,7 @@
 #include "file.h"
 #include "migration-stats.h"
 #include "multifd.h"
+#include "multifd-colo.h"
 #include "options.h"
 #include "migration.h"
 #include "qapi/error.h"
@@ -269,7 +270,6 @@ int multifd_ram_unfill_packet(MultiFDRecvParams *p, Error **errp)
         return -1;
     }
 
-    p->host = p->block->host;
     for (i = 0; i < p->normal_num; i++) {
         uint64_t offset = be64_to_cpu(packet->offset[i]);
 
@@ -294,6 +294,14 @@ int multifd_ram_unfill_packet(MultiFDRecvParams *p, Error **errp)
         p->zero[i] = offset;
     }
 
+    if (migrate_colo()) {
+        multifd_colo_prepare_recv(p);
+        assert(p->block->colo_cache);
+        p->host = p->block->colo_cache;
+    } else {
+        p->host = p->block->host;
+    }
+
     return 0;
 }
 

diff --git a/migration/multifd.c b/migration/multifd.c
index 4259ab2628c5f7b2a8502d3f6ab6a51b894b313e..2193088996f9ec42ff0c8783fb386b387b5dbf8b 100644 (file)
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -29,6 +29,7 @@
 #include "qemu-file.h"
 #include "trace.h"
 #include "multifd.h"
+#include "multifd-colo.h"
 #include "options.h"
 #include "qemu/yank.h"
 #include "io/channel-file.h"
@@ -1258,6 +1259,13 @@ static int multifd_ram_state_recv(MultiFDRecvParams *p, Error **errp)
     int ret;
 
     ret = multifd_recv_state->ops->recv(p, errp);
+    if (ret != 0) {
+        return ret;
+    }
+
+    if (migrate_colo()) {
+        multifd_colo_process_recv(p);
+    }
 
     return ret;
 }

diff --git a/migration/multifd.h b/migration/multifd.h
index 89a395aef2b09a6762c45b5361e0ab63256feff6..fbc35702b062fdc3213ce92baed35994f5967c2b 100644 (file)
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -279,7 +279,10 @@ typedef struct {
     uint64_t packets_recved;
     /* ramblock */
     RAMBlock *block;
-    /* ramblock host address */
+    /*
+     * Normally, it points to ramblock's host address.  When COLO
+     * is enabled, it points to the mirror cache for the ramblock.
+     */
     uint8_t *host;
     /* buffers to recv */
     struct iovec *iov;