Re: [Qemu-devel] [PATCH] migration: Improve bandwidth estimation

[Pierre Riteau]

Any comment on this patch?

On 31 mars 2011, at 22:30, Pierre Riteau wrote:

> In the current migration code, bandwidth is estimated by measuring the
> time spent in the ram_save_block loop and dividing by the number of sent
> bytes. However, because of buffering, the time spent in this loop is
> usually much less than the actual time required to send data on the
> wire. Try to improve this by measuring the time spent between two calls
> to ram_save_live instead.
> 
> Signed-off-by: Pierre Riteau <address@hidden>
> ---
> arch_init.c |    9 +++++++--
> 1 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index 0c09f91..7b822fe 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -175,6 +175,7 @@ static int ram_save_block(QEMUFile *f)
> }
> 
> static uint64_t bytes_transferred;
> +static int64_t prev_time;
> 
> static ram_addr_t ram_save_remaining(void)
> {
> @@ -254,6 +255,7 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
>     uint64_t bytes_transferred_last;
>     double bwidth = 0;
>     uint64_t expected_time = 0;
> +    int64_t current_time;
> 
>     if (stage < 0) {
>         cpu_physical_memory_set_dirty_tracking(0);
> @@ -286,6 +288,8 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
>         /* Enable dirty memory tracking */
>         cpu_physical_memory_set_dirty_tracking(1);
> 
> +        prev_time = qemu_get_clock_ns(rt_clock);
> +
>         qemu_put_be64(f, ram_bytes_total() | RAM_SAVE_FLAG_MEM_SIZE);
> 
>         QLIST_FOREACH(block, &ram_list.blocks, next) {
> @@ -296,7 +300,6 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
>     }
> 
>     bytes_transferred_last = bytes_transferred;
> -    bwidth = qemu_get_clock_ns(rt_clock);
> 
>     while (!qemu_file_rate_limit(f)) {
>         int bytes_sent;
> @@ -308,8 +311,10 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, 
> void *opaque)
>         }
>     }
> 
> -    bwidth = qemu_get_clock_ns(rt_clock) - bwidth;
> +    current_time = qemu_get_clock_ns(rt_clock);
> +    bwidth = current_time - prev_time;
>     bwidth = (bytes_transferred - bytes_transferred_last) / bwidth;
> +    prev_time = current_time;
> 
>     /* if we haven't transferred anything this round, force expected_time to a
>      * a very high value, but without crashing */
> -- 
> 1.7.4.2
> 

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