Re: [Qemu-devel] [PATCH COLO-Frame v11 18/39] COLO: Flush PVM's cached RAM into SVM's memory

[Dr. David Alan Gilbert]

* zhanghailiang (address@hidden) wrote:
> During the time of VM's running, PVM may dirty some pages, we will transfer
> PVM's dirty pages to SVM and store them into SVM's RAM cache at next 
> checkpoint
> time. So, the content of SVM's RAM cache will always be some with PVM's memory
> after checkpoint.
> 
> Instead of flushing all content of PVM's RAM cache into SVM's MEMORY,
> we do this in a more efficient way:
> Only flush any page that dirtied by PVM since last checkpoint.
> In this way, we can ensure SVM's memory same with PVM's.
> 
> Besides, we must ensure flush RAM cache before load device state.
> 
> Signed-off-by: zhanghailiang <address@hidden>
> Signed-off-by: Li Zhijian <address@hidden>
> Signed-off-by: Gonglei <address@hidden>
> ---
> v11:
> - Move the place of 'need_flush' (Dave's suggestion)
> - Remove unused 'DPRINTF("Flush ram_cache\n")'
> v10:
> - trace the number of dirty pages that be received.
> ---
>  include/migration/migration.h |  1 +
>  migration/colo.c              |  2 --
>  migration/ram.c               | 37 +++++++++++++++++++++++++++++++++++++
>  trace-events                  |  1 +
>  4 files changed, 39 insertions(+), 2 deletions(-)
> 
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index e41372d..221176b 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -336,4 +336,5 @@ PostcopyState postcopy_state_set(PostcopyState new_state);
>  /* ram cache */
>  int colo_init_ram_cache(void);
>  void colo_release_ram_cache(void);
> +void colo_flush_ram_cache(void);
>  #endif
> diff --git a/migration/colo.c b/migration/colo.c
> index 5ac8ff2..4095d97 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -385,8 +385,6 @@ void *colo_process_incoming_thread(void *opaque)
>          }
>          qemu_mutex_unlock_iothread();
>  
> -        /* TODO: flush vm state */
> -

Might have been better to put the TODO in a place that needed to be changed!

>          ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_VMSTATE_LOADED, 0);
>          if (ret < 0) {
>              goto out;
> diff --git a/migration/ram.c b/migration/ram.c
> index da6bbd6..4f37144 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2448,6 +2448,7 @@ static int ram_load(QEMUFile *f, void *opaque, int 
> version_id)
>       * be atomic
>       */
>      bool postcopy_running = postcopy_state_get() >= 
> POSTCOPY_INCOMING_LISTENING;
> +    bool need_flush = false;
>  
>      seq_iter++;
>  
> @@ -2482,6 +2483,7 @@ static int ram_load(QEMUFile *f, void *opaque, int 
> version_id)
>              /* After going into COLO, we should load the Page into 
> colo_cache */
>              if (ram_cache_enable) {
>                  host = colo_cache_from_block_offset(block, addr);
> +                need_flush = true;
>              } else {
>                  host = host_from_ram_block_offset(block, addr);
>              }
> @@ -2575,6 +2577,10 @@ static int ram_load(QEMUFile *f, void *opaque, int 
> version_id)
>      }
>  
>      rcu_read_unlock();
> +
> +    if (!ret  && ram_cache_enable && need_flush) {
> +        colo_flush_ram_cache();
> +    }
>      DPRINTF("Completed load of VM with exit code %d seq iteration "
>              "%" PRIu64 "\n", ret, seq_iter);
>      return ret;
> @@ -2647,6 +2653,37 @@ void colo_release_ram_cache(void)
>      rcu_read_unlock();
>  }
>  
> +/*
> + * Flush content of RAM cache into SVM's memory.
> + * Only flush the pages that be dirtied by PVM or SVM or both.
> + */
> +void colo_flush_ram_cache(void)
> +{
> +    RAMBlock *block = NULL;
> +    void *dst_host;
> +    void *src_host;
> +    ram_addr_t  offset = 0;
> +
> +    trace_colo_flush_ram_cache(migration_dirty_pages);
> +    rcu_read_lock();
> +    block = QLIST_FIRST_RCU(&ram_list.blocks);
> +    while (block) {
> +        ram_addr_t ram_addr_abs;
> +        offset = migration_bitmap_find_dirty(block, offset, &ram_addr_abs);
> +        migration_bitmap_clear_dirty(ram_addr_abs);
> +        if (offset >= block->used_length) {
> +            offset = 0;
> +            block = QLIST_NEXT_RCU(block, next);
> +        } else {
> +            dst_host = block->host + offset;
> +            src_host = block->colo_cache + offset;
> +            memcpy(dst_host, src_host, TARGET_PAGE_SIZE);
> +        }
> +    }
> +    rcu_read_unlock();

If you added a trace point here as well, it would make it very easy
to measure how long the flush was taking.

> +    assert(migration_dirty_pages == 0);
> +}
> +
>  static SaveVMHandlers savevm_ram_handlers = {
>      .save_live_setup = ram_save_setup,
>      .save_live_iterate = ram_save_iterate,
> diff --git a/trace-events b/trace-events
> index f8a0959..f158d2a 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -1264,6 +1264,7 @@ migration_throttle(void) ""
>  ram_load_postcopy_loop(uint64_t addr, int flags) "@%" PRIx64 " %x"
>  ram_postcopy_send_discard_bitmap(void) ""
>  ram_save_queue_pages(const char *rbname, size_t start, size_t len) "%s: 
> start: %zx len: %zx"
> +colo_flush_ram_cache(uint64_t dirty_pages) "dirty_pages %" PRIu64""

Minor; I think you can remove the "" at the end.

Other than  those minor things (and those double-space!):

Reviewed-by: Dr. David Alan Gilbert <address@hidden>

Dave

>  
>  # hw/display/qxl.c
>  disable qxl_interface_set_mm_time(int qid, uint32_t mm_time) "%d %d"
> -- 
> 1.8.3.1
> 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK