Re: [Qemu-devel] [PATCH 2/2] migration: Fix calculation of bytes_transferred

[Pierre Riteau]

Anyone interested by this diff?

On 12 mai 2010, at 15:12, Pierre Riteau wrote:

> When a page with all identical bytes is transferred, it is counted
> as a full page (TARGET_PAGE_SIZE) although only one byte is actually
> sent. Fix this by changing ram_save_block() to return the number of
> bytes sent instead of a boolean value. This makes bandwidth
> estimation, and consequently downtime estimation, more precise.
> 
> Signed-off-by: Pierre Riteau <address@hidden>
> ---
> arch_init.c |   21 ++++++++++++---------
> 1 files changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index cf6b7b0..76317af 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -108,7 +108,7 @@ static int ram_save_block(QEMUFile *f)
>     static ram_addr_t current_addr = 0;
>     ram_addr_t saved_addr = current_addr;
>     ram_addr_t addr = 0;
> -    int found = 0;
> +    int bytes_sent = 0;
> 
>     while (addr < last_ram_offset) {
>         if (cpu_physical_memory_get_dirty(current_addr, 
> MIGRATION_DIRTY_FLAG)) {
> @@ -123,19 +123,20 @@ static int ram_save_block(QEMUFile *f)
>             if (is_dup_page(p, *p)) {
>                 qemu_put_be64(f, current_addr | RAM_SAVE_FLAG_COMPRESS);
>                 qemu_put_byte(f, *p);
> +                bytes_sent = 1;
>             } else {
>                 qemu_put_be64(f, current_addr | RAM_SAVE_FLAG_PAGE);
>                 qemu_put_buffer(f, p, TARGET_PAGE_SIZE);
> +                bytes_sent = TARGET_PAGE_SIZE;
>             }
> 
> -            found = 1;
>             break;
>         }
>         addr += TARGET_PAGE_SIZE;
>         current_addr = (saved_addr + addr) % last_ram_offset;
>     }
> 
> -    return found;
> +    return bytes_sent;
> }
> 
> static uint64_t bytes_transferred;
> @@ -206,11 +207,11 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
>     bwidth = qemu_get_clock_ns(rt_clock);
> 
>     while (!qemu_file_rate_limit(f)) {
> -        int ret;
> +        int bytes_sent;
> 
> -        ret = ram_save_block(f);
> -        bytes_transferred += ret * TARGET_PAGE_SIZE;
> -        if (ret == 0) { /* no more blocks */
> +        bytes_sent = ram_save_block(f);
> +        bytes_transferred += bytes_sent;
> +        if (bytes_sent == 0) { /* no more blocks */
>             break;
>         }
>     }
> @@ -226,9 +227,11 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
> 
>     /* try transferring iterative blocks of memory */
>     if (stage == 3) {
> +        int bytes_sent;
> +
>         /* flush all remaining blocks regardless of rate limiting */
> -        while (ram_save_block(f) != 0) {
> -            bytes_transferred += TARGET_PAGE_SIZE;
> +        while ((bytes_sent = ram_save_block(f)) != 0) {
> +            bytes_transferred += bytes_sent;
>         }
>         cpu_physical_memory_set_dirty_tracking(0);
>     }
> -- 
> 1.7.1
> 
> 

-- 
Pierre Riteau -- PhD student, Myriads team, IRISA, Rennes, France
http://perso.univ-rennes1.fr/pierre.riteau/