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

[Hailiang Zhang]

On 2015/11/25 3:00, Dr. David Alan Gilbert wrote:
> * zhanghailiang (address@hidden) 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 <address@hidden>
> > Signed-off-by: Li Zhijian <address@hidden>
> > Signed-off-by: Gonglei <address@hidden>
> > Cc: Eric Blake <address@hidden>
> > ---
> > 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 / address@hidden / Manchester, UK
>
> .