Re: [PATCH v2 08/10] Reduce the PVM stop time during Checkpoint

[address@hidden]

On 3/12/21 1:03 PM, leirao wrote:
> From: "Rao, Lei" <lei.rao@intel.com>
>
> When flushing memory from ram cache to ram during every checkpoint
> on secondary VM, we can copy continuous chunks of memory instead of
> 4096 bytes per time to reduce the time of VM stop during checkpoint.
>
> Signed-off-by: Lei Rao <lei.rao@intel.com>
> ---
>   migration/ram.c | 44 +++++++++++++++++++++++++++++++++++++++++---
>   1 file changed, 41 insertions(+), 3 deletions(-)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index e795a8d..b269637 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -823,6 +823,39 @@ unsigned long migration_bitmap_find_dirty(RAMState *rs, 
> RAMBlock *rb,
>       return next;
>   }
>   
> +/*
> + * colo_bitmap_find_diry:find contiguous dirty pages from start
> + *
> + * Returns the page offset within memory region of the start of the 
> contiguout
> + * dirty page
> + *
> + * @rs: current RAM state
> + * @rb: RAMBlock where to search for dirty pages
> + * @start: page where we start the search
> + * @num: the number of contiguous dirty pages
> + */
> +static inline
> +unsigned long colo_bitmap_find_dirty(RAMState *rs, RAMBlock *rb,
> +                                     unsigned long start, unsigned long *num)
> +{
> +    unsigned long size = rb->used_length >> TARGET_PAGE_BITS;
> +    unsigned long *bitmap = rb->bmap;
> +    unsigned long first, next;
> +
> +    if (ramblock_is_ignored(rb)) {
> +        return size;
> +    }
> +
> +    first = find_next_bit(bitmap, size, start);
> +    if (first >= size) {
> +        return first;
> +    }
> +    next = find_next_zero_bit(bitmap, size, first + 1);
> +    assert(next >= first);
> +    *num = next - first;
> +    return first;

The idea is outstanding

i wonder it should return (next - 1) ?

Thanks
Zhijian


> +}
> +
>   static inline bool migration_bitmap_clear_dirty(RAMState *rs,
>                                                   RAMBlock *rb,
>                                                   unsigned long page)
> @@ -3669,6 +3702,8 @@ void colo_flush_ram_cache(void)
>       void *dst_host;
>       void *src_host;
>       unsigned long offset = 0;
> +    unsigned long num = 0;
> +    unsigned long i = 0;
>   
>       memory_global_dirty_log_sync();
>       WITH_RCU_READ_LOCK_GUARD() {
> @@ -3682,19 +3717,22 @@ void colo_flush_ram_cache(void)
>           block = QLIST_FIRST_RCU(&ram_list.blocks);
>   
>           while (block) {
> -            offset = migration_bitmap_find_dirty(ram_state, block, offset);
> +            offset = colo_bitmap_find_dirty(ram_state, block, offset, &num);
>   
>               if (((ram_addr_t)offset) << TARGET_PAGE_BITS
>                   >= block->used_length) {
>                   offset = 0;
> +                num = 0;
>                   block = QLIST_NEXT_RCU(block, next);
>               } else {
> -                migration_bitmap_clear_dirty(ram_state, block, offset);
> +                for (i = 0; i < num; i++) {
> +                    migration_bitmap_clear_dirty(ram_state, block, offset + 
> i);
> +                }
>                   dst_host = block->host
>                            + (((ram_addr_t)offset) << TARGET_PAGE_BITS);
>                   src_host = block->colo_cache
>                            + (((ram_addr_t)offset) << TARGET_PAGE_BITS);
> -                memcpy(dst_host, src_host, TARGET_PAGE_SIZE);
> +                memcpy(dst_host, src_host, TARGET_PAGE_SIZE * num);
>               }
>           }
>       }