Re: [Qemu-devel] [PATCH v8 4/6] migration/ram.c: add ram save state notifiers

[Peter Xu]

On Fri, Jun 08, 2018 at 04:10:41PM +0800, Wei Wang wrote:
> This patch adds a ram save state notifier list, and expose RAMState for
> the notifer callbacks to use.
> 
> Signed-off-by: Wei Wang <address@hidden>
> CC: Dr. David Alan Gilbert <address@hidden>
> CC: Juan Quintela <address@hidden>
> CC: Michael S. Tsirkin <address@hidden>
> CC: Peter Xu <address@hidden>
> ---
>  include/migration/misc.h | 52 +++++++++++++++++++++++++++++++++++++++
>  migration/ram.c          | 64 
> +++++++++++++++++-------------------------------
>  2 files changed, 75 insertions(+), 41 deletions(-)
> 
> diff --git a/include/migration/misc.h b/include/migration/misc.h
> index 113320e..b970d7d 100644
> --- a/include/migration/misc.h
> +++ b/include/migration/misc.h
> @@ -16,9 +16,61 @@
>  
>  #include "exec/cpu-common.h"
>  #include "qemu/notify.h"
> +#include "qemu/thread.h"
>  
>  /* migration/ram.c */
>  
> +typedef enum RamSaveState {
> +    RAM_SAVE_ERR = 0,
> +    RAM_SAVE_RESET = 1,
> +    RAM_SAVE_BEFORE_SYNC_BITMAP = 2,
> +    RAM_SAVE_AFTER_SYNC_BITMAP = 3,
> +    RAM_SAVE_MAX = 4,
> +} RamSaveState;
> +
> +/* State of RAM for migration */
> +typedef struct RAMState {
> +    /* QEMUFile used for this migration */
> +    QEMUFile *f;
> +    /* Last block that we have visited searching for dirty pages */
> +    RAMBlock *last_seen_block;
> +    /* Last block from where we have sent data */
> +    RAMBlock *last_sent_block;
> +    /* Last dirty target page we have sent */
> +    ram_addr_t last_page;
> +    /* last ram version we have seen */
> +    uint32_t last_version;
> +    /* We are in the first round */
> +    bool ram_bulk_stage;
> +    /* How many times we have dirty too many pages */
> +    int dirty_rate_high_cnt;
> +    /* ram save states used for notifiers */
> +    int ram_save_state;
> +    /* these variables are used for bitmap sync */
> +    /* last time we did a full bitmap_sync */
> +    int64_t time_last_bitmap_sync;
> +    /* bytes transferred at start_time */
> +    uint64_t bytes_xfer_prev;
> +    /* number of dirty pages since start_time */
> +    uint64_t num_dirty_pages_period;
> +    /* xbzrle misses since the beginning of the period */
> +    uint64_t xbzrle_cache_miss_prev;
> +    /* number of iterations at the beginning of period */
> +    uint64_t iterations_prev;
> +    /* Iterations since start */
> +    uint64_t iterations;
> +    /* number of dirty bits in the bitmap */
> +    uint64_t migration_dirty_pages;
> +    /* protects modification of the bitmap */
> +    QemuMutex bitmap_mutex;
> +    /* The RAMBlock used in the last src_page_requests */
> +    RAMBlock *last_req_rb;
> +    /* Queue of outstanding page requests from the destination */
> +    QemuMutex src_page_req_mutex;
> +    QSIMPLEQ_HEAD(src_page_requests, RAMSrcPageRequest) src_page_requests;
> +} RAMState;

Why move these chunk?  Can it be avoided?

> +
> +void add_ram_save_state_change_notifier(Notifier *notify);
>  void ram_mig_init(void);
>  void qemu_guest_free_page_hint(void *addr, size_t len);
>  
> diff --git a/migration/ram.c b/migration/ram.c
> index 237f11e..d45b5a4 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -56,6 +56,9 @@
>  #include "qemu/uuid.h"
>  #include "savevm.h"
>  
> +static NotifierList ram_save_state_notifiers =
> +    NOTIFIER_LIST_INITIALIZER(ram_save_state_notifiers);
> +
>  /***********************************************************/
>  /* ram save/restore */
>  
> @@ -267,49 +270,18 @@ struct RAMSrcPageRequest {
>      QSIMPLEQ_ENTRY(RAMSrcPageRequest) next_req;
>  };
>  
> -/* State of RAM for migration */
> -struct RAMState {
> -    /* QEMUFile used for this migration */
> -    QEMUFile *f;
> -    /* Last block that we have visited searching for dirty pages */
> -    RAMBlock *last_seen_block;
> -    /* Last block from where we have sent data */
> -    RAMBlock *last_sent_block;
> -    /* Last dirty target page we have sent */
> -    ram_addr_t last_page;
> -    /* last ram version we have seen */
> -    uint32_t last_version;
> -    /* We are in the first round */
> -    bool ram_bulk_stage;
> -    /* How many times we have dirty too many pages */
> -    int dirty_rate_high_cnt;
> -    /* these variables are used for bitmap sync */
> -    /* last time we did a full bitmap_sync */
> -    int64_t time_last_bitmap_sync;
> -    /* bytes transferred at start_time */
> -    uint64_t bytes_xfer_prev;
> -    /* number of dirty pages since start_time */
> -    uint64_t num_dirty_pages_period;
> -    /* xbzrle misses since the beginning of the period */
> -    uint64_t xbzrle_cache_miss_prev;
> -    /* number of iterations at the beginning of period */
> -    uint64_t iterations_prev;
> -    /* Iterations since start */
> -    uint64_t iterations;
> -    /* number of dirty bits in the bitmap */
> -    uint64_t migration_dirty_pages;
> -    /* protects modification of the bitmap */
> -    QemuMutex bitmap_mutex;
> -    /* The RAMBlock used in the last src_page_requests */
> -    RAMBlock *last_req_rb;
> -    /* Queue of outstanding page requests from the destination */
> -    QemuMutex src_page_req_mutex;
> -    QSIMPLEQ_HEAD(src_page_requests, RAMSrcPageRequest) src_page_requests;
> -};
> -typedef struct RAMState RAMState;
> -
>  static RAMState *ram_state;
>  
> +void add_ram_save_state_change_notifier(Notifier *notify)
> +{
> +    notifier_list_add(&ram_save_state_notifiers, notify);
> +}
> +
> +static void notify_ram_save_state_change_notifier(void)
> +{
> +    notifier_list_notify(&ram_save_state_notifiers, ram_state);
> +}
> +
>  uint64_t ram_bytes_remaining(void)
>  {
>      return ram_state ? (ram_state->migration_dirty_pages * TARGET_PAGE_SIZE) 
> :
> @@ -1139,6 +1111,9 @@ static void migration_bitmap_sync(RAMState *rs)
>      int64_t end_time;
>      uint64_t bytes_xfer_now;
>  
> +    rs->ram_save_state = RAM_SAVE_BEFORE_SYNC_BITMAP;

What's the point to keep this state after all?...

> +    notify_ram_save_state_change_notifier();
> +
>      ram_counters.dirty_sync_count++;
>  
>      if (!rs->time_last_bitmap_sync) {
> @@ -1205,6 +1180,9 @@ static void migration_bitmap_sync(RAMState *rs)
>      if (migrate_use_events()) {
>          qapi_event_send_migration_pass(ram_counters.dirty_sync_count, NULL);
>      }
> +
> +    rs->ram_save_state = RAM_SAVE_AFTER_SYNC_BITMAP;
> +    notify_ram_save_state_change_notifier();
>  }
>  
>  /**
> @@ -1961,6 +1939,8 @@ static void ram_state_reset(RAMState *rs)
>      rs->last_page = 0;
>      rs->last_version = ram_list.version;
>      rs->ram_bulk_stage = true;
> +    rs->ram_save_state = RAM_SAVE_RESET;

... and this state is much more meaningless afaict ...

> +    notify_ram_save_state_change_notifier();
>  }
>  
>  #define MAX_WAIT 50 /* ms, half buffered_file limit */
> @@ -2709,6 +2689,8 @@ out:
>  
>      ret = qemu_file_get_error(f);
>      if (ret < 0) {
> +        rs->ram_save_state = RAM_SAVE_ERR;
> +        notify_ram_save_state_change_notifier();
>          return ret;
>      }

Also, I would prefer to add a general event framework for migration
rather than "ram save" specific.  Then we add SYNC_START/SYNC_END
events.  These notifiers aren't a lot, it'll be a bit awkward to
introduce the framework multiple times for similar purpuse (after we
have a common notifier we can merge the postcopy notifiers AFAIU).

Regards,

-- 
Peter Xu