[PATCH v7 09/12] migration/multifd: Enable DSA offloading in multifd sender path.

[Yichen Wang <yichen.wang@bytedance.com>]

From: Hao Xiang <hao.xiang@linux.dev>

Multifd sender path gets an array of pages queued by the migration
thread. It performs zero page checking on every page in the array.
The pages are classfied as either a zero page or a normal page. This
change uses Intel DSA to offload the zero page checking from CPU to
the DSA accelerator. The sender thread submits a batch of pages to DSA
hardware and waits for the DSA completion thread to signal for work
completion.

Signed-off-by: Hao Xiang <hao.xiang@linux.dev>
Signed-off-by: Yichen Wang <yichen.wang@bytedance.com>
---
 migration/multifd-zero-page.c | 129 ++++++++++++++++++++++++++++++----
 migration/multifd.c           |  29 +++++++-
 migration/multifd.h           |   5 ++
 3 files changed, 147 insertions(+), 16 deletions(-)

diff --git a/migration/multifd-zero-page.c b/migration/multifd-zero-page.c
index f1e988a959..639aed9f6b 100644
--- a/migration/multifd-zero-page.c
+++ b/migration/multifd-zero-page.c
@@ -21,7 +21,9 @@
 
 static bool multifd_zero_page_enabled(void)
 {
-    return migrate_zero_page_detection() == ZERO_PAGE_DETECTION_MULTIFD;
+    ZeroPageDetection curMethod = migrate_zero_page_detection();
+    return (curMethod == ZERO_PAGE_DETECTION_MULTIFD ||
+            curMethod == ZERO_PAGE_DETECTION_DSA_ACCEL);
 }
 
 static void swap_page_offset(ram_addr_t *pages_offset, int a, int b)
@@ -37,26 +39,49 @@ static void swap_page_offset(ram_addr_t *pages_offset, int a, int b)
     pages_offset[b] = temp;
 }
 
+#ifdef CONFIG_DSA_OPT
+
+static void swap_result(bool *results, int a, int b)
+{
+    bool temp;
+
+    if (a == b) {
+        return;
+    }
+
+    temp = results[a];
+    results[a] = results[b];
+    results[b] = temp;
+}
+
 /**
- * multifd_send_zero_page_detect: Perform zero page detection on all pages.
+ * zero_page_detect_dsa: Perform zero page detection using
+ * Intel Data Streaming Accelerator (DSA).
  *
- * Sorts normal pages before zero pages in p->pages->offset and updates
- * p->pages->normal_num.
+ * Sorts normal pages before zero pages in pages->offset and updates
+ * pages->normal_num.
  *
  * @param p A pointer to the send params.
  */
-void multifd_send_zero_page_detect(MultiFDSendParams *p)
+static void zero_page_detect_dsa(MultiFDSendParams *p)
 {
     MultiFDPages_t *pages = &p->data->u.ram;
     RAMBlock *rb = pages->block;
-    int i = 0;
-    int j = pages->num - 1;
+    bool *results = p->dsa_batch_task->results;
 
-    if (!multifd_zero_page_enabled()) {
-        pages->normal_num = pages->num;
-        goto out;
+    for (int i = 0; i < pages->num; i++) {
+        p->dsa_batch_task->addr[i] =
+            (ram_addr_t)(rb->host + pages->offset[i]);
     }
 
+    buffer_is_zero_dsa_batch_sync(p->dsa_batch_task,
+                                  (const void **)p->dsa_batch_task->addr,
+                                  pages->num,
+                                  multifd_ram_page_size());
+
+    int i = 0;
+    int j = pages->num - 1;
+
     /*
      * Sort the page offset array by moving all normal pages to
      * the left and all zero pages to the right of the array.
@@ -64,23 +89,39 @@ void multifd_send_zero_page_detect(MultiFDSendParams *p)
     while (i <= j) {
         uint64_t offset = pages->offset[i];
 
-        if (!buffer_is_zero(rb->host + offset, multifd_ram_page_size())) {
+        if (!results[i]) {
             i++;
             continue;
         }
 
+        swap_result(results, i, j);
         swap_page_offset(pages->offset, i, j);
         ram_release_page(rb->idstr, offset);
         j--;
     }
 
     pages->normal_num = i;
+}
 
-out:
-    stat64_add(&mig_stats.normal_pages, pages->normal_num);
-    stat64_add(&mig_stats.zero_pages, pages->num - pages->normal_num);
+void multifd_dsa_cleanup(void)
+{
+    qemu_dsa_cleanup();
+}
+
+#else
+
+static void zero_page_detect_dsa(MultiFDSendParams *p)
+{
+    g_assert_not_reached();
+}
+
+void multifd_dsa_cleanup(void)
+{
+    return ;
 }
 
+#endif
+
 void multifd_recv_zero_page_process(MultiFDRecvParams *p)
 {
     for (int i = 0; i < p->zero_num; i++) {
@@ -92,3 +133,63 @@ void multifd_recv_zero_page_process(MultiFDRecvParams *p)
         }
     }
 }
+
+/**
+ * zero_page_detect_cpu: Perform zero page detection using CPU.
+ *
+ * Sorts normal pages before zero pages in p->pages->offset and updates
+ * p->pages->normal_num.
+ *
+ * @param p A pointer to the send params.
+ */
+static void zero_page_detect_cpu(MultiFDSendParams *p)
+{
+    MultiFDPages_t *pages = &p->data->u.ram;
+    RAMBlock *rb = pages->block;
+    int i = 0;
+    int j = pages->num - 1;
+
+    /*
+     * Sort the page offset array by moving all normal pages to
+     * the left and all zero pages to the right of the array.
+     */
+    while (i <= j) {
+        uint64_t offset = pages->offset[i];
+
+        if (!buffer_is_zero(rb->host + offset, multifd_ram_page_size())) {
+            i++;
+            continue;
+        }
+
+        swap_page_offset(pages->offset, i, j);
+        ram_release_page(rb->idstr, offset);
+        j--;
+    }
+
+    pages->normal_num = i;
+}
+
+/**
+ * multifd_send_zero_page_detect: Perform zero page detection on all pages.
+ *
+ * @param p A pointer to the send params.
+ */
+void multifd_send_zero_page_detect(MultiFDSendParams *p)
+{
+    MultiFDPages_t *pages = &p->data->u.ram;
+
+    if (!multifd_zero_page_enabled()) {
+        pages->normal_num = pages->num;
+        goto out;
+    }
+
+    if (qemu_dsa_is_running()) {
+        zero_page_detect_dsa(p);
+    } else {
+        zero_page_detect_cpu(p);
+    }
+
+out:
+    stat64_add(&mig_stats.normal_pages, pages->normal_num);
+    stat64_add(&mig_stats.zero_pages, pages->num - pages->normal_num);
+}
diff --git a/migration/multifd.c b/migration/multifd.c
index 4374e14a96..689acceff2 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -13,6 +13,7 @@
 #include "qemu/osdep.h"
 #include "qemu/cutils.h"
 #include "qemu/rcu.h"
+#include "qemu/dsa.h"
 #include "exec/target_page.h"
 #include "sysemu/sysemu.h"
 #include "exec/ramblock.h"
@@ -462,6 +463,8 @@ static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
     p->name = NULL;
     g_free(p->data);
     p->data = NULL;
+    buffer_zero_batch_task_destroy(p->dsa_batch_task);
+    p->dsa_batch_task = NULL;
     p->packet_len = 0;
     g_free(p->packet);
     p->packet = NULL;
@@ -493,6 +496,8 @@ void multifd_send_shutdown(void)
 
     multifd_send_terminate_threads();
 
+    multifd_dsa_cleanup();
+
     for (i = 0; i < migrate_multifd_channels(); i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
         Error *local_err = NULL;
@@ -814,11 +819,31 @@ bool multifd_send_setup(void)
     uint32_t page_count = multifd_ram_page_count();
     bool use_packets = multifd_use_packets();
     uint8_t i;
+    Error *local_err = NULL;
 
     if (!migrate_multifd()) {
         return true;
     }
 
+    if (s &&
+        s->parameters.zero_page_detection == ZERO_PAGE_DETECTION_DSA_ACCEL) {
+        // Populate the dsa device path from accel-path
+        const strList *accel_path = migrate_accel_path();
+        g_autofree strList *dsa_parameter = g_malloc0(sizeof(strList));
+        strList **tail = &dsa_parameter;
+        while (accel_path) {
+            if (strncmp(accel_path->value, "dsa:", 4) == 0) {
+                QAPI_LIST_APPEND(tail, &accel_path->value[4]);
+            }
+            accel_path = accel_path->next;
+        }
+        if (qemu_dsa_init(dsa_parameter, &local_err)) {
+            ret = -1;
+        } else {
+            qemu_dsa_start();
+        }
+    }
+
     thread_count = migrate_multifd_channels();
     multifd_send_state = g_malloc0(sizeof(*multifd_send_state));
     multifd_send_state->params = g_new0(MultiFDSendParams, thread_count);
@@ -829,12 +854,12 @@ bool multifd_send_setup(void)
 
     for (i = 0; i < thread_count; i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
-        Error *local_err = NULL;
 
         qemu_sem_init(&p->sem, 0);
         qemu_sem_init(&p->sem_sync, 0);
         p->id = i;
         p->data = multifd_send_data_alloc();
+        p->dsa_batch_task = buffer_zero_batch_task_init(page_count);
 
         if (use_packets) {
             p->packet_len = sizeof(MultiFDPacket_t)
@@ -865,7 +890,6 @@ bool multifd_send_setup(void)
 
     for (i = 0; i < thread_count; i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
-        Error *local_err = NULL;
 
         ret = multifd_send_state->ops->send_setup(p, &local_err);
         if (ret) {
@@ -1047,6 +1071,7 @@ void multifd_recv_cleanup(void)
             qemu_thread_join(&p->thread);
         }
     }
+    multifd_dsa_cleanup();
     for (i = 0; i < migrate_multifd_channels(); i++) {
         multifd_recv_cleanup_channel(&multifd_recv_state->params[i]);
     }
diff --git a/migration/multifd.h b/migration/multifd.h
index 50d58c0c9c..e293ddbc1d 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -15,6 +15,7 @@
 
 #include "exec/target_page.h"
 #include "ram.h"
+#include "qemu/dsa.h"
 
 typedef struct MultiFDRecvData MultiFDRecvData;
 typedef struct MultiFDSendData MultiFDSendData;
@@ -155,6 +156,9 @@ typedef struct {
     bool pending_sync;
     MultiFDSendData *data;
 
+    /* Zero page checking batch task */
+    QemuDsaBatchTask *dsa_batch_task;
+
     /* thread local variables. No locking required */
 
     /* pointer to the packet */
@@ -313,6 +317,7 @@ void multifd_send_fill_packet(MultiFDSendParams *p);
 bool multifd_send_prepare_common(MultiFDSendParams *p);
 void multifd_send_zero_page_detect(MultiFDSendParams *p);
 void multifd_recv_zero_page_process(MultiFDRecvParams *p);
+void multifd_dsa_cleanup(void);
 
 static inline void multifd_send_prepare_header(MultiFDSendParams *p)
 {
-- 
Yichen Wang