Re: [Qemu-devel] [PATCH COLO-Frame v11 10/39] COLO: Implement colo checkpoint protocol

[Hailiang Zhang <zhang.zhanghailiang@huawei.com>]

On 2015/11/25 3:00, Dr. David Alan Gilbert wrote:
> * 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
>>                                                         initial work
>> 'checkpoint-ready'     <------------------------------ @
>>
>> 'checkpoint-request'   @ ----------------------------->
>>                                                         Suspend (Only in hybrid mode)
>> 'checkpoint-reply'     <------------------------------ @
>>                         Suspend&Save state
>> 'vmstate-send'         @ ----------------------------->
>>                         Send state                      Receive state
>> 'vmstate-received'     <------------------------------ @
>>                         Release packets                 Load state
>> 'vmstate-load'         <------------------------------ @
>>                         Resume                          Resume (Only in hybrid mode)
>>
>>                         Start Comparing (Only 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>
>> ---
>> v11:
>> - Add missing 'checkpoint-ready' communication in comment.
>> - Use parameter to return 'value' for colo_ctl_get() (Dave's suggestion)
>> - Fix trace for colo_ctl_get() to trace command and value both
>> v10:
>> - Rename enum COLOCmd to COLOCommand (Eric's suggestion).
>> - Remove unused 'ram-steal'
>> ---
>>   migration/colo.c | 198 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>   qapi-schema.json |  27 ++++++++
>>   trace-events     |   2 +
>>   3 files changed, 225 insertions(+), 2 deletions(-)
>>
>> diff --git a/migration/colo.c b/migration/colo.c
>> index 0ab9618..c045d61 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)
>>   {
>> @@ -34,9 +36,107 @@ 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, got cmd:%d", *cmd);
>> +        return -EINVAL;
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +static int colo_ctl_get(QEMUFile *f, uint32_t require, uint64_t *value)
>> +{
>> +    int ret;
>> +    uint32_t cmd;
>> +
>> +    ret = colo_ctl_get_cmd(f, &cmd);
>> +    if (ret < 0) {
>> +        return ret;
>> +    }
>> +    if (cmd != require) {
>> +        error_report("Unexpect colo command, expect:%d, but got cmd:%d",
>> +                     require, cmd);
>
> I think you need to use PRIu32 rather than %d  since they are uint32_t
> (I doubt it will break on anything, but it's correct).
>

>> +        return -EINVAL;
>> +    }
>> +
>> +    *value = qemu_get_be64(f);
>> +    trace_colo_ctl_get(COLOCommand_lookup[cmd], *value);
>> +    ret = qemu_file_get_error(f);
>> +
>> +    return ret;
>> +}
>> +
>> +static int colo_do_checkpoint_transaction(MigrationState *s)
>> +{
>> +    int ret;
>> +    uint64_t value;
>> +
>> +    ret = colo_ctl_put(s->to_dst_file, COLO_COMMAND_CHECKPOINT_REQUEST, 0);
>> +    if (ret < 0) {
>> +        goto out;
>> +    }
>> +
>> +    ret = colo_ctl_get(s->rp_state.from_dst_file,
>> +                       COLO_COMMAND_CHECKPOINT_REPLY, &value);
>> +    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->rp_state.from_dst_file,
>> +                       COLO_COMMAND_VMSTATE_RECEIVED, &value);
>> +    if (ret < 0) {
>> +        goto out;
>> +    }
>> +
>> +    ret = colo_ctl_get(s->rp_state.from_dst_file,
>> +                       COLO_COMMAND_VMSTATE_LOADED, &value);
>> +    if (ret < 0) {
>> +        goto out;
>> +    }
>> +
>> +    /* TODO: resume Primary */
>> +
>> +out:
>> +    return ret;
>> +}
>> +
>>   static void colo_process_checkpoint(MigrationState *s)
>>   {
>>       int ret = 0;
>> +    uint64_t value;
>>
>>       s->rp_state.from_dst_file = qemu_file_get_return_path(s->to_dst_file);
>>       if (!s->rp_state.from_dst_file) {
>> @@ -45,12 +145,28 @@ 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->rp_state.from_dst_file,
>> +                       COLO_COMMAND_CHECKPOINT_READY, &value);
>> +    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) {
>> @@ -73,10 +189,46 @@ 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 ?
>> +     */
>
> You could use something simple like an incrementing value, if you just
> wanted to make it a little more robust against problems.
>

Hmm, this a good choice, but we have to hold a variable to record the increasing
value.
Checking the length of the corresponding commands' string seems better. :)

>> +    value = qemu_get_be64(f);
>> +    if (value != 0) {
>> +        error_report("Got unexpected value %" PRIu64 " for '%s' command",
>> +                     value, COLOCommand_lookup[cmd]);
>> +        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;
>>       int ret = 0;
>> +    uint64_t value;
>>
>>       migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
>>                         MIGRATION_STATUS_COLO);
>> @@ -93,7 +245,49 @@ void *colo_process_incoming_thread(void *opaque)
>>       */
>>       qemu_set_block(qemu_get_fd(mis->from_src_file));
>>
>> -    /* 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;
>> +            }
>> +        }
>> +        /* FIXME: This is unnecessary for periodic checkpoint mode */
>> +        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,
>> +                           &value);
>> +        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 c2f3b63..48a87af 100644
>> --- a/qapi-schema.json
>> +++ b/qapi-schema.json
>> @@ -722,6 +722,33 @@
>>   { 'command': 'migrate-start-postcopy' }
>>
>>   ##
>> +# @COLOCommand
>> +#
>> +# The commands for COLO fault tolerance
>> +#
>> +# @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: 2.6
>> +##
>> +{ '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 c98d473..f8a0959 100644
>> --- a/trace-events
>> +++ b/trace-events
>> @@ -1579,6 +1579,8 @@ postcopy_ram_incoming_cleanup_join(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, uint64_t value) "Receive '%s' cmd, value: %" PRIu64""
>
> I don't think you need the "" at the end of the line
>

OK, will fix in next version.

Thanks,
Hailiang

> Dave
>
>>
>>   # 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
>
> .
>