Re: [Qemu-devel] [PATCH COLO-Frame v10 09/38] COLO: Implement colo checkpoint protocol

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

* zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
> We need communications protocol of user-defined to control the checkpoint
> process.
> 
> The new checkpoint request is started by Primary VM, and the interactive process
> like below:
> Checkpoint synchronizing points,
> 
>                        Primary                         Secondary
> 'checkpoint-request'   @ ----------------------------->
>                                                        Suspend (In hybrid mode)
> 'checkpoint-reply'     <------------------------------ @
>                        Suspend&Save state

Why is this initial pair necessary?  Can't you just start with the vmstate-send
and save the extra request pair/round trip?  On the 2nd checkpoint we know
the SVM already received the previous checkpoint because we got it's first
vmstate-load.

I guess in full-COLO (rather than simple checkpoint) you can get the secondary to
do some of it's stopping/cleanup after it sends the checkpoint-reply
but before vmstate-send, so you can hide some of the time.

(Perhaps add a comment to explain)

> 'vmstate-send'         @ ----------------------------->
>                        Send state                      Receive state
> 'vmstate-received'     <------------------------------ @
>                        Release packets                 Load state
> 'vmstate-load'         <------------------------------ @
>                        Resume                          Resume (In hybrid mode)
> 
>                        Start Comparing (In hybrid mode)
> NOTE:
>  1) '@' who sends the message
>  2) Every sync-point is synchronized by two sides with only
>     one handshake(single direction) for low-latency.
>     If more strict synchronization is required, a opposite direction
>     sync-point should be added.
>  3) Since sync-points are single direction, the remote side may
>     go forward a lot when this side just receives the sync-point.
>  4) For now, we only support 'periodic' checkpoint, for which
>    the Secondary VM is not running, later we will support 'hybrid' mode.
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> Cc: Eric Blake <eblake@redhat.com>
> ---
> v10:
> - Rename enum COLOCmd to COLOCommand (Eric's suggestion).
> - Remove unused 'ram-steal'
> ---
>  migration/colo.c | 192 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  qapi-schema.json |  27 ++++++++
>  trace-events     |   2 +
>  3 files changed, 219 insertions(+), 2 deletions(-)
> 
> diff --git a/migration/colo.c b/migration/colo.c
> index 4fdf3a9..2510762 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -10,10 +10,12 @@
>   * later.  See the COPYING file in the top-level directory.
>   */
>  
> +#include <unistd.h>
>  #include "sysemu/sysemu.h"
>  #include "migration/colo.h"
>  #include "trace.h"
>  #include "qemu/error-report.h"
> +#include "qemu/sockets.h"
>  
>  bool colo_supported(void)
>  {
> @@ -34,6 +36,103 @@ bool migration_incoming_in_colo_state(void)
>      return mis && (mis->state == MIGRATION_STATUS_COLO);
>  }
>  
> +/* colo checkpoint control helper */
> +static int colo_ctl_put(QEMUFile *f, uint32_t cmd, uint64_t value)
> +{
> +    int ret = 0;
> +
> +    qemu_put_be32(f, cmd);
> +    qemu_put_be64(f, value);
> +    qemu_fflush(f);
> +
> +    ret = qemu_file_get_error(f);
> +    trace_colo_ctl_put(COLOCommand_lookup[cmd], value);
> +
> +    return ret;
> +}
> +
> +static int colo_ctl_get_cmd(QEMUFile *f, uint32_t *cmd)
> +{
> +    int ret = 0;
> +
> +    *cmd = qemu_get_be32(f);
> +    ret = qemu_file_get_error(f);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +    if (*cmd >= COLO_COMMAND_MAX) {
> +        error_report("Invalid colo command, get cmd:%d", *cmd);
> +        return -EINVAL;
> +    }
> +    trace_colo_ctl_get(COLOCommand_lookup[*cmd]);
> +
> +    return 0;
> +}
> +
> +static int colo_ctl_get(QEMUFile *f, uint32_t require)
> +{
> +    int ret;
> +    uint32_t cmd;
> +    uint64_t value;
> +
> +    ret = colo_ctl_get_cmd(f, &cmd);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +    if (cmd != require) {
> +        error_report("Unexpect colo command, expect:%d, but get cmd:%d",
> +                     require, cmd);
> +        return -EINVAL;
> +    }
> +
> +    value = qemu_get_be64(f);
> +    ret = qemu_file_get_error(f);
> +    if (ret < 0) {
> +        return ret;
> +    }
> +
> +    return value;
> +}

Should the return type be uint64_t since you're returning value?
But then you're also using it to return an error code; so perhaps
it might be better to have a     uint64_t *value    parameter to
return the value separately; or define the range that the value
can actually take.

(Also very minor typo: 'got' not 'get' in a few errors)

> +static int colo_do_checkpoint_transaction(MigrationState *s)
> +{
> +    int ret;
> +
> +    ret = colo_ctl_put(s->to_dst_file, COLO_COMMAND_CHECKPOINT_REQUEST, 0);
> +    if (ret < 0) {
> +        goto out;
> +    }
> +
> +    ret = colo_ctl_get(s->from_dst_file, COLO_COMMAND_CHECKPOINT_REPLY);
> +    if (ret < 0) {
> +        goto out;
> +    }
> +
> +    /* TODO: suspend and save vm state to colo buffer */
> +
> +    ret = colo_ctl_put(s->to_dst_file, COLO_COMMAND_VMSTATE_SEND, 0);
> +    if (ret < 0) {
> +        goto out;
> +    }
> +
> +    /* TODO: send vmstate to Secondary */
> +
> +    ret = colo_ctl_get(s->from_dst_file, COLO_COMMAND_VMSTATE_RECEIVED);
> +    if (ret < 0) {
> +        goto out;
> +    }> +
> +    ret = colo_ctl_get(s->from_dst_file, COLO_COMMAND_VMSTATE_LOADED);
> +    if (ret < 0) {
> +        goto out;
> +    }
> +
> +    /* TODO: resume Primary */
> +
> +out:
> +    return ret;
> +}
> +
>  static void colo_process_checkpoint(MigrationState *s)
>  {
>      int fd, ret = 0;
> @@ -51,12 +150,27 @@ static void colo_process_checkpoint(MigrationState *s)
>          goto out;
>      }
>  
> +    /*
> +     * Wait for Secondary finish loading vm states and enter COLO
> +     * restore.
> +     */
> +    ret = colo_ctl_get(s->from_dst_file, COLO_COMMAND_CHECKPOINT_READY);
> +    if (ret < 0) {
> +        goto out;
> +    }
> +
>      qemu_mutex_lock_iothread();
>      vm_start();
>      qemu_mutex_unlock_iothread();
>      trace_colo_vm_state_change("stop", "run");
>  
> -    /*TODO: COLO checkpoint savevm loop*/
> +    while (s->state == MIGRATION_STATUS_COLO) {
> +        /* start a colo checkpoint */
> +        ret = colo_do_checkpoint_transaction(s);
> +        if (ret < 0) {
> +            goto out;
> +        }
> +    }
>  
>  out:
>      if (ret < 0) {
> @@ -79,6 +193,39 @@ void migrate_start_colo_process(MigrationState *s)
>      qemu_mutex_lock_iothread();
>  }
>  
> +/*
> + * return:
> + * 0: start a checkpoint
> + * -1: some error happened, exit colo restore
> + */
> +static int colo_wait_handle_cmd(QEMUFile *f, int *checkpoint_request)
> +{
> +    int ret;
> +    uint32_t cmd;
> +    uint64_t value;
> +
> +    ret = colo_ctl_get_cmd(f, &cmd);
> +    if (ret < 0) {
> +        /* do failover ? */
> +        return ret;
> +    }
> +    /* Fix me: this value should be 0, which is not so good,
> +     * should be used for checking ?
> +     */
> +    value = qemu_get_be64(f);
> +    if (value != 0) {

should output error message as well?

> +        return -EINVAL;
> +    }
> +
> +    switch (cmd) {
> +    case COLO_COMMAND_CHECKPOINT_REQUEST:
> +        *checkpoint_request = 1;
> +        return 0;
> +    default:
> +        return -EINVAL;
> +    }
> +}
> +
>  void *colo_process_incoming_thread(void *opaque)
>  {
>      MigrationIncomingState *mis = opaque;
> @@ -98,7 +245,48 @@ void *colo_process_incoming_thread(void *opaque)
>          error_report("colo incoming thread: Open QEMUFile to_src_file failed");
>          goto out;
>      }
> -    /* TODO: COLO checkpoint restore loop */
> +
> +    ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_CHECKPOINT_READY, 0);
> +    if (ret < 0) {
> +        goto out;
> +    }
> +
> +    while (mis->state == MIGRATION_STATUS_COLO) {
> +        int request = 0;
> +        int ret = colo_wait_handle_cmd(mis->from_src_file, &request);
> +
> +        if (ret < 0) {
> +            break;
> +        } else {
> +            if (!request) {
> +                continue;
> +            }
> +        }
> +
> +        ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_CHECKPOINT_REPLY, 0);
> +        if (ret < 0) {
> +            goto out;
> +        }
> +
> +        ret = colo_ctl_get(mis->from_src_file, COLO_COMMAND_VMSTATE_SEND);
> +        if (ret < 0) {
> +            goto out;
> +        }
> +
> +        /* TODO: read migration data into colo buffer */
> +
> +        ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_VMSTATE_RECEIVED, 0);
> +        if (ret < 0) {
> +            goto out;
> +        }
> +
> +        /* TODO: load vm state */
> +
> +        ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_VMSTATE_LOADED, 0);
> +        if (ret < 0) {
> +            goto out;
> +        }
> +    }
>  
>  out:
>      if (ret < 0) {
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 22251ec..5c4fe6d 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -702,6 +702,33 @@
>              '*tls-port': 'int', '*cert-subject': 'str' } }
>  
>  ##
> +# @COLOCommand
> +#
> +# The colo command
> +#
> +# @invalid: unknown command
> +#
> +# @checkpoint-ready: SVM is ready for checkpointing
> +#
> +# @checkpoint-request: PVM tells SVM to prepare for new checkpointing
> +#
> +# @checkpoint-reply: SVM gets PVM's checkpoint request
> +#
> +# @vmstate-send: VM's state will be sent by PVM.
> +#
> +# @vmstate-size: The total size of VMstate.
> +#
> +# @vmstate-received: VM's state has been received by SVM
> +#
> +# @vmstate-loaded: VM's state has been loaded by SVM
> +#
> +# Since: 2.5
> +##
> +{ 'enum': 'COLOCommand',
> +  'data': [ 'invalid', 'checkpoint-ready', 'checkpoint-request',
> +            'checkpoint-reply', 'vmstate-send', 'vmstate-size',
> +            'vmstate-received', 'vmstate-loaded' ] }
> +
>  # @MouseInfo:
>  #
>  # Information about a mouse device.
> diff --git a/trace-events b/trace-events
> index 9cd6391..ee4679c 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -1499,6 +1499,8 @@ rdma_start_outgoing_migration_after_rdma_source_init(void) ""
>  
>  # migration/colo.c
>  colo_vm_state_change(const char *old, const char *new) "Change '%s' => '%s'"
> +colo_ctl_put(const char *msg, uint64_t value) "Send '%s' cmd, value: %" PRIu64""
> +colo_ctl_get(const char *msg) "Receive '%s' cmd"
>  
>  # kvm-all.c
>  kvm_ioctl(int type, void *arg) "type 0x%x, arg %p"
> -- 
> 1.8.3.1
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK