[PATCH v2 13/20] migration/multifd: Prepare to introduce DSA acceleration on the multifd path.

[Hao Xiang]

1. Refactor multifd_send_thread function.
2. Implement buffer_is_zero_use_cpu to handle CPU based zero page
checking.
3. Introduce the batch task structure in MultiFDSendParams.

Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
---
 migration/multifd.c | 82 ++++++++++++++++++++++++++++++++++++---------
 migration/multifd.h |  3 ++
 2 files changed, 70 insertions(+), 15 deletions(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index 1198ffde9c..68ab97f918 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -14,6 +14,8 @@
 #include "qemu/cutils.h"
 #include "qemu/rcu.h"
 #include "qemu/cutils.h"
+#include "qemu/dsa.h"
+#include "qemu/memalign.h"
 #include "exec/target_page.h"
 #include "sysemu/sysemu.h"
 #include "exec/ramblock.h"
@@ -574,6 +576,11 @@ void multifd_save_cleanup(void)
         p->name = NULL;
         multifd_pages_clear(p->pages);
         p->pages = NULL;
+        g_free(p->addr);
+        p->addr = NULL;
+        buffer_zero_batch_task_destroy(p->batch_task);
+        qemu_vfree(p->batch_task);
+        p->batch_task = NULL;
         p->packet_len = 0;
         g_free(p->packet);
         p->packet = NULL;
@@ -678,13 +685,66 @@ int multifd_send_sync_main(QEMUFile *f)
     return 0;
 }
 
+static void set_page(MultiFDSendParams *p, bool zero_page, uint64_t offset)
+{
+    RAMBlock *rb = p->pages->block;
+    if (zero_page) {
+        p->zero[p->zero_num] = offset;
+        p->zero_num++;
+        ram_release_page(rb->idstr, offset);
+    } else {
+        p->normal[p->normal_num] = offset;
+        p->normal_num++;
+    }
+}
+
+static void buffer_is_zero_use_cpu(MultiFDSendParams *p)
+{
+    const void **buf = (const void **)p->addr;
+    assert(!migrate_use_main_zero_page());
+
+    for (int i = 0; i < p->pages->num; i++) {
+        p->batch_task->results[i] = buffer_is_zero(buf[i], p->page_size);
+    }
+}
+
+static void set_normal_pages(MultiFDSendParams *p)
+{
+    for (int i = 0; i < p->pages->num; i++) {
+        p->batch_task->results[i] = false;
+    }
+}
+
+static void multifd_zero_page_check(MultiFDSendParams *p)
+{
+    /* older qemu don't understand zero page on multifd channel */
+    bool use_multifd_zero_page = !migrate_use_main_zero_page();
+
+    RAMBlock *rb = p->pages->block;
+
+    for (int i = 0; i < p->pages->num; i++) {
+        p->addr[i] = (ram_addr_t)(rb->host + p->pages->offset[i]);
+    }
+
+    if (use_multifd_zero_page) {
+        buffer_is_zero_use_cpu(p);
+    } else {
+        // No zero page checking. All pages are normal pages.
+        set_normal_pages(p);
+    }
+
+    for (int i = 0; i < p->pages->num; i++) {
+        uint64_t offset = p->pages->offset[i];
+        bool zero_page = p->batch_task->results[i];
+        set_page(p, zero_page, offset);
+    }
+}
+
 static void *multifd_send_thread(void *opaque)
 {
     MultiFDSendParams *p = opaque;
     MigrationThread *thread = NULL;
     Error *local_err = NULL;
-    /* qemu older than 8.2 don't understand zero page on multifd channel */
-    bool use_multifd_zero_page = !migrate_use_main_zero_page();
     int ret = 0;
     bool use_zero_copy_send = migrate_zero_copy_send();
 
@@ -710,7 +770,6 @@ static void *multifd_send_thread(void *opaque)
         qemu_mutex_lock(&p->mutex);
 
         if (p->pending_job) {
-            RAMBlock *rb = p->pages->block;
             uint64_t packet_num = p->packet_num;
             uint32_t flags;
 
@@ -723,18 +782,7 @@ static void *multifd_send_thread(void *opaque)
                 p->iovs_num = 1;
             }
 
-            for (int i = 0; i < p->pages->num; i++) {
-                uint64_t offset = p->pages->offset[i];
-                if (use_multifd_zero_page &&
-                    buffer_is_zero(rb->host + offset, p->page_size)) {
-                    p->zero[p->zero_num] = offset;
-                    p->zero_num++;
-                    ram_release_page(rb->idstr, offset);
-                } else {
-                    p->normal[p->normal_num] = offset;
-                    p->normal_num++;
-                }
-            }
+            multifd_zero_page_check(p);
 
             if (p->normal_num) {
                 ret = multifd_send_state->ops->send_prepare(p, &local_err);
@@ -976,6 +1024,10 @@ int multifd_save_setup(Error **errp)
         p->pending_job = 0;
         p->id = i;
         p->pages = multifd_pages_init(page_count);
+        p->addr = g_new0(ram_addr_t, page_count);
+        p->batch_task =
+            (struct buffer_zero_batch_task *)qemu_memalign(64, 
sizeof(*p->batch_task));
+        buffer_zero_batch_task_init(p->batch_task, page_count);
         p->packet_len = sizeof(MultiFDPacket_t)
                       + sizeof(uint64_t) * page_count;
         p->packet = g_malloc0(p->packet_len);
diff --git a/migration/multifd.h b/migration/multifd.h
index 13762900d4..62f31b03c0 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -119,6 +119,9 @@ typedef struct {
      * pending_job != 0 -> multifd_channel can use it.
      */
     MultiFDPages_t *pages;
+    /* Address of each pages in pages */
+    ram_addr_t *addr;
+    struct buffer_zero_batch_task *batch_task;
 
     /* thread local variables. No locking required */
 
-- 
2.30.2