[RFC PATCH v1 19/26] migration/multifd: Add pages to the receiving side

[Fabiano Rosas]

Currently multifd does not need to have knowledge of pages on the
receiving side because all the information needed is within the
packets that come in the stream.

We're about to add support to fixed-ram migration, which cannot use
packets because it expects the ramblock section in the migration file
to contain only the guest pages data.

Add a pointer to MultiFDPages in the multifd_recv_state and use the
pages similarly to what we already do on the sending side. The pages
are used to transfer data between the ram migration code in the main
migration thread and the multifd receiving threads.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 migration/multifd.c | 98 +++++++++++++++++++++++++++++++++++++++++++++
 migration/multifd.h | 12 ++++++
 2 files changed, 110 insertions(+)

diff --git a/migration/multifd.c b/migration/multifd.c
index 1332b426ce..20ef665218 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -1004,6 +1004,8 @@ int multifd_save_setup(Error **errp)
 
 struct {
     MultiFDRecvParams *params;
+    /* array of pages to receive */
+    MultiFDPages_t *pages;
     /* number of created threads */
     int count;
     /* syncs main thread and channels */
@@ -1014,6 +1016,66 @@ struct {
     MultiFDMethods *ops;
 } *multifd_recv_state;
 
+static int multifd_recv_pages(QEMUFile *f)
+{
+    int i;
+    static int next_recv_channel;
+    MultiFDRecvParams *p = NULL;
+    MultiFDPages_t *pages = multifd_recv_state->pages;
+
+    /*
+     * next_channel can remain from a previous migration that was
+     * using more channels, so ensure it doesn't overflow if the
+     * limit is lower now.
+     */
+    next_recv_channel %= migrate_multifd_channels();
+    for (i = next_recv_channel;; i = (i + 1) % migrate_multifd_channels()) {
+        p = &multifd_recv_state->params[i];
+
+        qemu_mutex_lock(&p->mutex);
+        if (p->quit) {
+            error_report("%s: channel %d has already quit!", __func__, i);
+            qemu_mutex_unlock(&p->mutex);
+            return -1;
+        }
+        if (!p->pending_job) {
+            p->pending_job++;
+            next_recv_channel = (i + 1) % migrate_multifd_channels();
+            break;
+        }
+        qemu_mutex_unlock(&p->mutex);
+    }
+
+    multifd_recv_state->pages = p->pages;
+    p->pages = pages;
+    qemu_mutex_unlock(&p->mutex);
+    qemu_sem_post(&p->sem);
+
+    return 1;
+}
+
+int multifd_recv_queue_page(QEMUFile *f, RAMBlock *block, ram_addr_t offset)
+{
+    MultiFDPages_t *pages = multifd_recv_state->pages;
+
+    if (!pages->block) {
+        pages->block = block;
+    }
+
+    pages->offset[pages->num] = offset;
+    pages->num++;
+
+    if (pages->num < pages->allocated) {
+        return 1;
+    }
+
+    if (multifd_recv_pages(f) < 0) {
+        return -1;
+    }
+
+    return 1;
+}
+
 static void multifd_recv_terminate_threads(Error *err)
 {
     int i;
@@ -1035,6 +1097,7 @@ static void multifd_recv_terminate_threads(Error *err)
 
         qemu_mutex_lock(&p->mutex);
         p->quit = true;
+        qemu_sem_post(&p->sem);
         /*
          * We could arrive here for two reasons:
          *  - normal quit, i.e. everything went fine, just finished
@@ -1083,9 +1146,12 @@ void multifd_load_cleanup(void)
         object_unref(OBJECT(p->c));
         p->c = NULL;
         qemu_mutex_destroy(&p->mutex);
+        qemu_sem_destroy(&p->sem);
         qemu_sem_destroy(&p->sem_sync);
         g_free(p->name);
         p->name = NULL;
+        multifd_pages_clear(p->pages);
+        p->pages = NULL;
         p->packet_len = 0;
         g_free(p->packet);
         p->packet = NULL;
@@ -1098,6 +1164,8 @@ void multifd_load_cleanup(void)
     qemu_sem_destroy(&multifd_recv_state->sem_sync);
     g_free(multifd_recv_state->params);
     multifd_recv_state->params = NULL;
+    multifd_pages_clear(multifd_recv_state->pages);
+    multifd_recv_state->pages = NULL;
     g_free(multifd_recv_state);
     multifd_recv_state = NULL;
 }
@@ -1160,6 +1228,25 @@ static void *multifd_recv_thread(void *opaque)
                 break;
             }
             p->num_packets++;
+        } else {
+            /*
+             * No packets, so we need to wait for the vmstate code to
+             * queue pages.
+             */
+            qemu_sem_wait(&p->sem);
+            qemu_mutex_lock(&p->mutex);
+            if (!p->pending_job) {
+                qemu_mutex_unlock(&p->mutex);
+                break;
+            }
+
+            for (int i = 0; i < p->pages->num; i++) {
+                p->normal[p->normal_num] = p->pages->offset[i];
+                p->normal_num++;
+            }
+
+            p->pages->num = 0;
+            p->host = p->pages->block->host;
         }
 
         flags = p->flags;
@@ -1182,6 +1269,13 @@ static void *multifd_recv_thread(void *opaque)
             qemu_sem_post(&multifd_recv_state->sem_sync);
             qemu_sem_wait(&p->sem_sync);
         }
+
+        if (!use_packets) {
+            qemu_mutex_lock(&p->mutex);
+            p->pending_job--;
+            p->pages->block = NULL;
+            qemu_mutex_unlock(&p->mutex);
+        }
     }
 
     if (local_err) {
@@ -1216,6 +1310,7 @@ int multifd_load_setup(Error **errp)
     thread_count = migrate_multifd_channels();
     multifd_recv_state = g_malloc0(sizeof(*multifd_recv_state));
     multifd_recv_state->params = g_new0(MultiFDRecvParams, thread_count);
+    multifd_recv_state->pages = multifd_pages_init(page_count);
     qatomic_set(&multifd_recv_state->count, 0);
     qemu_sem_init(&multifd_recv_state->sem_sync, 0);
     multifd_recv_state->ops = multifd_ops[migrate_multifd_compression()];
@@ -1224,9 +1319,12 @@ int multifd_load_setup(Error **errp)
         MultiFDRecvParams *p = &multifd_recv_state->params[i];
 
         qemu_mutex_init(&p->mutex);
+        qemu_sem_init(&p->sem, 0);
         qemu_sem_init(&p->sem_sync, 0);
         p->quit = false;
+        p->pending_job = 0;
         p->id = i;
+        p->pages = multifd_pages_init(page_count);
 
         if (use_packets) {
             p->packet_len = sizeof(MultiFDPacket_t)
diff --git a/migration/multifd.h b/migration/multifd.h
index 354150ff55..2f008217c3 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -24,6 +24,7 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error **errp);
 void multifd_recv_sync_main(void);
 int multifd_send_sync_main(QEMUFile *f);
 int multifd_queue_page(QEMUFile *f, RAMBlock *block, ram_addr_t offset);
+int multifd_recv_queue_page(QEMUFile *f, RAMBlock *block, ram_addr_t offset);
 
 /* Multifd Compression flags */
 #define MULTIFD_FLAG_SYNC (1 << 0)
@@ -153,7 +154,11 @@ typedef struct {
     uint32_t page_size;
     /* number of pages in a full packet */
     uint32_t page_count;
+    /* multifd flags for receiving ram */
+    int read_flags;
 
+    /* sem where to wait for more work */
+    QemuSemaphore sem;
     /* syncs main thread and channels */
     QemuSemaphore sem_sync;
 
@@ -167,6 +172,13 @@ typedef struct {
     uint32_t flags;
     /* global number of generated multifd packets */
     uint64_t packet_num;
+    int pending_job;
+    /* array of pages to sent.
+     * The owner of 'pages' depends of 'pending_job' value:
+     * pending_job == 0 -> migration_thread can use it.
+     * pending_job != 0 -> multifd_channel can use it.
+     */
+    MultiFDPages_t *pages;
 
     /* thread local variables. No locking required */
 
-- 
2.35.3