Re: [Qemu-devel] [PATCH] migration: Fix rate limiting issue on RDMA migration

[Juan Quintela <quintela@redhat.com>]

Lidong Chen <jemmy858585@gmail.com> wrote:
> RDMA migration implement save_page function for QEMUFile, but
> ram_control_save_page do not increase bytes_xfer. So when doing
> RDMA migration, it will use whole bandwidth.
>
> Signed-off-by: Lidong Chen <lidongchen@tencent.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>

This part of the code is a mess.

To answer David:
- pos: Where we need to write that bit of stuff
- bytex_xfer: how much have we written

WHen we are doing snapshots on qcow2, we store memory in a contiguous
piece of memory, so we can "overwrite" that "page" if a new verion
cames. Nothing else (except the block) uses te "pos" parameter, so we
can't not trust on it.

And that  has been for a fast look at the code, that I got really
confused (again).



> ---
>  migration/qemu-file.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> index 2ab2bf3..217609d 100644
> --- a/migration/qemu-file.c
> +++ b/migration/qemu-file.c
> @@ -253,7 +253,7 @@ size_t ram_control_save_page(QEMUFile *f, ram_addr_t block_offset,
>      if (f->hooks && f->hooks->save_page) {
>          int ret = f->hooks->save_page(f, f->opaque, block_offset,
>                                        offset, size, bytes_sent);
> -
> +        f->bytes_xfer += size;
>          if (ret != RAM_SAVE_CONTROL_DELAYED) {
>              if (bytes_sent && *bytes_sent > 0) {
>                  qemu_update_position(f, *bytes_sent);