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[PATCH v8 3/7] migration: enable multifd and postcopy together

Prasad Pandit posted 7 patches 2 weeks, 1 day ago
[PATCH v8 3/7] migration: enable multifd and postcopy together
Posted by Prasad Pandit 2 weeks, 1 day ago 
From: Prasad Pandit <pjp@fedoraproject.org>

Enable Multifd and Postcopy migration together.
The migration_ioc_process_incoming() routine
checks magic value sent on each channel and
helps to properly setup multifd and postcopy
channels.

The Precopy and Multifd threads work during the
initial guest RAM transfer. When migration moves
to the Postcopy phase, the multifd threads cease
to send data on multifd channels and Postcopy
threads on the destination request/pull data from
the source side.

Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
---
 migration/multifd-nocomp.c | 3 ++-
 migration/multifd.c        | 7 +++++++
 migration/options.c        | 5 -----
 migration/ram.c            | 7 +++----
 4 files changed, 12 insertions(+), 10 deletions(-)

v8:
- Separate this patch out from earlier patch-2.

v7:
- https://lore.kernel.org/qemu-devel/20250228121749.553184-1-ppandit@redhat.com/T/#t

diff --git a/migration/multifd-nocomp.c b/migration/multifd-nocomp.c
index ffe75256c9..02f8bf8ce8 100644
--- a/migration/multifd-nocomp.c
+++ b/migration/multifd-nocomp.c
@@ -17,6 +17,7 @@
 #include "migration-stats.h"
 #include "multifd.h"
 #include "options.h"
+#include "migration.h"
 #include "qapi/error.h"
 #include "qemu/cutils.h"
 #include "qemu/error-report.h"
@@ -399,7 +400,7 @@ int multifd_ram_flush_and_sync(QEMUFile *f)
     MultiFDSyncReq req;
     int ret;
 
-    if (!migrate_multifd()) {
+    if (!migrate_multifd() || migration_in_postcopy()) {
         return 0;
     }
 
diff --git a/migration/multifd.c b/migration/multifd.c
index 6139cabe44..074d16d07d 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -1379,6 +1379,13 @@ static void *multifd_recv_thread(void *opaque)
         }
 
         if (has_data) {
+            /*
+             * multifd thread should not be active and receive data
+             * when migration is in the Postcopy phase. Two threads
+             * writing the same memory area could easily corrupt
+             * the guest state.
+             */
+            assert(!migration_in_postcopy());
             if (is_device_state) {
                 assert(use_packets);
                 ret = multifd_device_state_recv(p, &local_err);
diff --git a/migration/options.c b/migration/options.c
index b0ac2ea408..48aa6076de 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -491,11 +491,6 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
             error_setg(errp, "Postcopy is not compatible with ignore-shared");
             return false;
         }
-
-        if (new_caps[MIGRATION_CAPABILITY_MULTIFD]) {
-            error_setg(errp, "Postcopy is not yet compatible with multifd");
-            return false;
-        }
     }
 
     if (new_caps[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]) {
diff --git a/migration/ram.c b/migration/ram.c
index 424df6d9f1..6fd88cbf2a 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1297,7 +1297,7 @@ static int find_dirty_block(RAMState *rs, PageSearchStatus *pss)
         pss->page = 0;
         pss->block = QLIST_NEXT_RCU(pss->block, next);
         if (!pss->block) {
-            if (multifd_ram_sync_per_round()) {
+            if (multifd_ram_sync_per_round() && !migration_in_postcopy()) {
                 QEMUFile *f = rs->pss[RAM_CHANNEL_PRECOPY].pss_channel;
                 int ret = multifd_ram_flush_and_sync(f);
                 if (ret < 0) {
@@ -1976,9 +1976,8 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss)
         }
     }
 
-    if (migrate_multifd()) {
-        RAMBlock *block = pss->block;
-        return ram_save_multifd_page(block, offset);
+    if (migrate_multifd() && !migration_in_postcopy()) {
+        return ram_save_multifd_page(pss->block, offset);
     }
 
     return ram_save_page(rs, pss);
-- 
2.48.1
Re: [PATCH v8 3/7] migration: enable multifd and postcopy together
Posted by Fabiano Rosas 2 days, 18 hours ago 
Prasad Pandit <ppandit@redhat.com> writes:

> From: Prasad Pandit <pjp@fedoraproject.org>
>
> Enable Multifd and Postcopy migration together.
> The migration_ioc_process_incoming() routine
> checks magic value sent on each channel and
> helps to properly setup multifd and postcopy
> channels.
>
> The Precopy and Multifd threads work during the
> initial guest RAM transfer. When migration moves
> to the Postcopy phase, the multifd threads cease
> to send data on multifd channels and Postcopy
> threads on the destination request/pull data from
> the source side.
>
> Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
> ---
>  migration/multifd-nocomp.c | 3 ++-
>  migration/multifd.c        | 7 +++++++
>  migration/options.c        | 5 -----
>  migration/ram.c            | 7 +++----
>  4 files changed, 12 insertions(+), 10 deletions(-)
>
> v8:
> - Separate this patch out from earlier patch-2.
>
> v7:
> - https://lore.kernel.org/qemu-devel/20250228121749.553184-1-ppandit@redhat.com/T/#t
>
> diff --git a/migration/multifd-nocomp.c b/migration/multifd-nocomp.c
> index ffe75256c9..02f8bf8ce8 100644
> --- a/migration/multifd-nocomp.c
> +++ b/migration/multifd-nocomp.c
> @@ -17,6 +17,7 @@
>  #include "migration-stats.h"
>  #include "multifd.h"
>  #include "options.h"
> +#include "migration.h"
>  #include "qapi/error.h"
>  #include "qemu/cutils.h"
>  #include "qemu/error-report.h"
> @@ -399,7 +400,7 @@ int multifd_ram_flush_and_sync(QEMUFile *f)
>      MultiFDSyncReq req;
>      int ret;
>  
> -    if (!migrate_multifd()) {
> +    if (!migrate_multifd() || migration_in_postcopy()) {
>          return 0;
>      }
>  
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 6139cabe44..074d16d07d 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -1379,6 +1379,13 @@ static void *multifd_recv_thread(void *opaque)
>          }
>  
>          if (has_data) {
> +            /*
> +             * multifd thread should not be active and receive data
> +             * when migration is in the Postcopy phase. Two threads
> +             * writing the same memory area could easily corrupt
> +             * the guest state.
> +             */
> +            assert(!migration_in_postcopy());
>              if (is_device_state) {
>                  assert(use_packets);
>                  ret = multifd_device_state_recv(p, &local_err);
> diff --git a/migration/options.c b/migration/options.c
> index b0ac2ea408..48aa6076de 100644
> --- a/migration/options.c
> +++ b/migration/options.c
> @@ -491,11 +491,6 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
>              error_setg(errp, "Postcopy is not compatible with ignore-shared");
>              return false;
>          }
> -
> -        if (new_caps[MIGRATION_CAPABILITY_MULTIFD]) {
> -            error_setg(errp, "Postcopy is not yet compatible with multifd");
> -            return false;
> -        }
>      }
>  
>      if (new_caps[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]) {
> diff --git a/migration/ram.c b/migration/ram.c
> index 424df6d9f1..6fd88cbf2a 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1297,7 +1297,7 @@ static int find_dirty_block(RAMState *rs, PageSearchStatus *pss)
>          pss->page = 0;
>          pss->block = QLIST_NEXT_RCU(pss->block, next);
>          if (!pss->block) {
> -            if (multifd_ram_sync_per_round()) {
> +            if (multifd_ram_sync_per_round() && !migration_in_postcopy()) {

I'd rather not put this check here. multifd_ram_flush_and_sync() will
already return 0 if in postcopy.

>                  QEMUFile *f = rs->pss[RAM_CHANNEL_PRECOPY].pss_channel;
>                  int ret = multifd_ram_flush_and_sync(f);
>                  if (ret < 0) {
> @@ -1976,9 +1976,8 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss)
>          }
>      }
>  
> -    if (migrate_multifd()) {
> -        RAMBlock *block = pss->block;
> -        return ram_save_multifd_page(block, offset);
> +    if (migrate_multifd() && !migration_in_postcopy()) {
> +        return ram_save_multifd_page(pss->block, offset);
>      }
>  
>      return ram_save_page(rs, pss);

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