Re: [Qemu-devel] [PATCH 1/8] migration: stop compressing page in migration thread

[Dr. David Alan Gilbert]

* address@hidden (address@hidden) wrote:
> From: Xiao Guangrong <address@hidden>
> 
> As compression is a heavy work, do not do it in migration thread,
> instead, we post it out as a normal page
> 
> Signed-off-by: Xiao Guangrong <address@hidden>
> ---
>  migration/ram.c | 32 ++++++++++++++++----------------

Hi,
  Do you have some performance numbers to show this helps?  Were those
taken on a normal system or were they taken with one of the compression
accelerators (which I think the compression migration was designed for)?

>  1 file changed, 16 insertions(+), 16 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 7266351fd0..615693f180 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1132,7 +1132,7 @@ static int ram_save_compressed_page(RAMState *rs, 
> PageSearchStatus *pss,
>      int pages = -1;
>      uint64_t bytes_xmit = 0;
>      uint8_t *p;
> -    int ret, blen;
> +    int ret;
>      RAMBlock *block = pss->block;
>      ram_addr_t offset = pss->page << TARGET_PAGE_BITS;
>  
> @@ -1162,23 +1162,23 @@ static int ram_save_compressed_page(RAMState *rs, 
> PageSearchStatus *pss,
>          if (block != rs->last_sent_block) {
>              flush_compressed_data(rs);
>              pages = save_zero_page(rs, block, offset);
> -            if (pages == -1) {
> -                /* Make sure the first page is sent out before other pages */
> -                bytes_xmit = save_page_header(rs, rs->f, block, offset |
> -                                              RAM_SAVE_FLAG_COMPRESS_PAGE);
> -                blen = qemu_put_compression_data(rs->f, p, TARGET_PAGE_SIZE,
> -                                                 migrate_compress_level());
> -                if (blen > 0) {
> -                    ram_counters.transferred += bytes_xmit + blen;
> -                    ram_counters.normal++;
> -                    pages = 1;
> -                } else {
> -                    qemu_file_set_error(rs->f, blen);
> -                    error_report("compressed data failed!");
> -                }
> -            }
>              if (pages > 0) {
>                  ram_release_pages(block->idstr, offset, pages);
> +            } else {
> +                /*
> +                 * Make sure the first page is sent out before other pages.
> +                 *
> +                 * we post it as normal page as compression will take much
> +                 * CPU resource.
> +                 */
> +                ram_counters.transferred += save_page_header(rs, rs->f, 
> block,
> +                                                offset | RAM_SAVE_FLAG_PAGE);
> +                qemu_put_buffer_async(rs->f, p, TARGET_PAGE_SIZE,
> +                                      migrate_release_ram() &
> +                                      migration_in_postcopy());
> +                ram_counters.transferred += TARGET_PAGE_SIZE;
> +                ram_counters.normal++;
> +                pages = 1;


However, the code and idea look OK, so

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

>              }
>          } else {
>              pages = save_zero_page(rs, block, offset);
> -- 
> 2.14.3
> 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK