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

[Wang, Lei]

On 11/14/2023 13:40, Hao Xiang wrote:> 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.

Please pay attention to the comment style here and in other patches.

> +        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 */

s/pages/page

> +    ram_addr_t *addr;

I think there is not need to introduce this variable since is can be simply
derived by:

        p->addr[i] = (ram_addr_t)(rb->host + p->pages->offset[i]);

and it is useless when we check the zero page in main thread (main-zero-page=y)

> +    struct buffer_zero_batch_task *batch_task;
>  
>      /* thread local variables. No locking required */
>