Re: [Qemu-devel] [RFC PATCH v4 23/28] COLO: Improve checkpoint efficiency by do additional periodic checkpoint

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
> Besides normal checkpoint which according to the result of net packets
> comparing, We do additional checkpoint periodically, it will reduce the number
> of dirty pages when do one checkpoint, if we don't do checkpoint for a long
> time (This is a special case when the net packets is always consistent).
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
> ---
>  migration/colo.c | 29 +++++++++++++++++++++--------
>  1 file changed, 21 insertions(+), 8 deletions(-)
> 
> diff --git a/migration/colo.c b/migration/colo.c
> index 9ef4554..da5bc5e 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -10,6 +10,7 @@
>   * later.  See the COPYING file in the top-level directory.
>   */
>  
> +#include "qemu/timer.h"
>  #include "sysemu/sysemu.h"
>  #include "migration/migration-colo.h"
>  #include "qemu/error-report.h"
> @@ -32,6 +33,13 @@
>  */
>  #define CHECKPOINT_MIN_PERIOD 100  /* unit: ms */
>  
> +/*
> + * force checkpoint timer: unit ms
> + * this is large because COLO checkpoint will mostly depend on
> + * COLO compare module.
> + */
> +#define CHECKPOINT_MAX_PEROID 10000
> +
>  enum {
>      COLO_READY = 0x46,
>  
> @@ -340,14 +348,7 @@ static void *colo_thread(void *opaque)
>          proxy_checkpoint_req = colo_proxy_compare();
>          if (proxy_checkpoint_req < 0) {
>              goto out;
> -        } else if (!proxy_checkpoint_req) {
> -            /*
> -             * No checkpoint is needed, wait for 1ms and then
> -             * check if we need checkpoint again
> -             */
> -            g_usleep(1000);
> -            continue;
> -        } else {
> +        } else if (proxy_checkpoint_req) {
>              int64_t interval;
>  
>              current_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
> @@ -357,8 +358,20 @@ static void *colo_thread(void *opaque)
>                  g_usleep((1000*(CHECKPOINT_MIN_PERIOD - interval)));
>              }
>              DPRINTF("Net packets is not consistent!!!\n");
> +            goto do_checkpoint;
> +        }
> +
> +        /*
> +         * No proxy checkpoint is request, wait for 100ms
> +         * and then check if we need checkpoint again.
> +         */
> +        current_time = qemu_clock_get_ms(QEMU_CLOCK_HOST);
> +        if (current_time - checkpoint_time < CHECKPOINT_MAX_PEROID) {
> +            g_usleep(100000);
> +            continue;

This 100ms sleep is interesting - can you explain it's purpose; is it
just to save CPU time in the colo thread?  It used to be 1ms (above
and in the previous version).

The MIN_PERIOD already stops the checkpoints being too close together,
so this is a separate sleep from that.

Dave

>          }
>  
> +do_checkpoint:
>          /* start a colo checkpoint */
>          if (colo_do_checkpoint_transaction(s, colo_control)) {
>              goto out;
> -- 
> 1.7.12.4
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK