Re: [PATCH v3 13/24] migration/multifd: Device state transfer support - send side

[Fabiano Rosas <farosas@suse.de>]

"Maciej S. Szmigiero" <mail@maciej.szmigiero.name> writes:

> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>
> A new function multifd_queue_device_state() is provided for device to queue
> its state for transmission via a multifd channel.
>
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> ---
>  include/migration/misc.h         |   4 ++
>  migration/meson.build            |   1 +
>  migration/multifd-device-state.c | 106 +++++++++++++++++++++++++++++++
>  migration/multifd-nocomp.c       |  11 +++-
>  migration/multifd.c              |  43 +++++++++++--
>  migration/multifd.h              |  24 ++++---
>  6 files changed, 173 insertions(+), 16 deletions(-)
>  create mode 100644 migration/multifd-device-state.c
>
> diff --git a/include/migration/misc.h b/include/migration/misc.h
> index c92ca018ab3b..118e205bbcc6 100644
> --- a/include/migration/misc.h
> +++ b/include/migration/misc.h
> @@ -109,4 +109,8 @@ bool migration_incoming_postcopy_advised(void);
>  /* True if background snapshot is active */
>  bool migration_in_bg_snapshot(void);
>  
> +/* migration/multifd-device-state.c */
> +bool multifd_queue_device_state(char *idstr, uint32_t instance_id,
> +                                char *data, size_t len);
> +
>  #endif
> diff --git a/migration/meson.build b/migration/meson.build
> index d53cf3417ab8..9788c47bb56e 100644
> --- a/migration/meson.build
> +++ b/migration/meson.build
> @@ -22,6 +22,7 @@ system_ss.add(files(
>    'migration-hmp-cmds.c',
>    'migration.c',
>    'multifd.c',
> +  'multifd-device-state.c',
>    'multifd-nocomp.c',
>    'multifd-zlib.c',
>    'multifd-zero-page.c',
> diff --git a/migration/multifd-device-state.c b/migration/multifd-device-state.c
> new file mode 100644
> index 000000000000..7741a64fbd4d
> --- /dev/null
> +++ b/migration/multifd-device-state.c
> @@ -0,0 +1,106 @@
> +/*
> + * Multifd device state migration
> + *
> + * Copyright (C) 2024 Oracle and/or its affiliates.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu/lockable.h"
> +#include "migration/misc.h"
> +#include "multifd.h"
> +
> +static QemuMutex queue_job_mutex;
> +
> +static MultiFDSendData *device_state_send;
> +
> +size_t multifd_device_state_payload_size(void)
> +{
> +    return sizeof(MultiFDDeviceState_t);
> +}
> +
> +void multifd_device_state_send_setup(void)
> +{
> +    qemu_mutex_init(&queue_job_mutex);
> +
> +    device_state_send = multifd_send_data_alloc();
> +}
> +
> +void multifd_device_state_clear(MultiFDDeviceState_t *device_state)
> +{
> +    g_clear_pointer(&device_state->idstr, g_free);
> +    g_clear_pointer(&device_state->buf, g_free);
> +}
> +
> +void multifd_device_state_send_cleanup(void)
> +{
> +    g_clear_pointer(&device_state_send, multifd_send_data_free);
> +
> +    qemu_mutex_destroy(&queue_job_mutex);
> +}
> +
> +static void multifd_device_state_fill_packet(MultiFDSendParams *p)
> +{
> +    MultiFDDeviceState_t *device_state = &p->data->u.device_state;
> +    MultiFDPacketDeviceState_t *packet = p->packet_device_state;
> +
> +    packet->hdr.flags = cpu_to_be32(p->flags);
> +    strncpy(packet->idstr, device_state->idstr, sizeof(packet->idstr));
> +    packet->instance_id = cpu_to_be32(device_state->instance_id);
> +    packet->next_packet_size = cpu_to_be32(p->next_packet_size);
> +}
> +
> +static void multifd_prepare_header_device_state(MultiFDSendParams *p)
> +{
> +    p->iov[0].iov_len = sizeof(*p->packet_device_state);
> +    p->iov[0].iov_base = p->packet_device_state;
> +    p->iovs_num++;
> +}
> +
> +void multifd_device_state_send_prepare(MultiFDSendParams *p)
> +{
> +    MultiFDDeviceState_t *device_state = &p->data->u.device_state;
> +
> +    assert(multifd_payload_device_state(p->data));
> +
> +    multifd_prepare_header_device_state(p);
> +
> +    assert(!(p->flags & MULTIFD_FLAG_SYNC));
> +
> +    p->next_packet_size = device_state->buf_len;
> +    if (p->next_packet_size > 0) {
> +        p->iov[p->iovs_num].iov_base = device_state->buf;
> +        p->iov[p->iovs_num].iov_len = p->next_packet_size;
> +        p->iovs_num++;
> +    }
> +
> +    p->flags |= MULTIFD_FLAG_NOCOMP | MULTIFD_FLAG_DEVICE_STATE;
> +
> +    multifd_device_state_fill_packet(p);
> +}
> +
> +bool multifd_queue_device_state(char *idstr, uint32_t instance_id,
> +                                char *data, size_t len)
> +{
> +    /* Device state submissions can come from multiple threads */
> +    QEMU_LOCK_GUARD(&queue_job_mutex);
> +    MultiFDDeviceState_t *device_state;
> +
> +    assert(multifd_payload_empty(device_state_send));
> +
> +    multifd_set_payload_type(device_state_send, MULTIFD_PAYLOAD_DEVICE_STATE);
> +    device_state = &device_state_send->u.device_state;
> +    device_state->idstr = g_strdup(idstr);
> +    device_state->instance_id = instance_id;
> +    device_state->buf = g_memdup2(data, len);
> +    device_state->buf_len = len;
> +
> +    if (!multifd_send(&device_state_send)) {
> +        multifd_send_data_clear(device_state_send);
> +        return false;
> +    }
> +
> +    return true;
> +}
> diff --git a/migration/multifd-nocomp.c b/migration/multifd-nocomp.c
> index fa0fd0289eca..23564ce9aea9 100644
> --- a/migration/multifd-nocomp.c
> +++ b/migration/multifd-nocomp.c
> @@ -84,6 +84,13 @@ static void multifd_nocomp_send_cleanup(MultiFDSendParams *p, Error **errp)
>      return;
>  }
>  
> +static void multifd_ram_prepare_header(MultiFDSendParams *p)
> +{
> +    p->iov[0].iov_len = p->packet_len;
> +    p->iov[0].iov_base = p->packet;
> +    p->iovs_num++;
> +}
> +
>  static void multifd_send_prepare_iovs(MultiFDSendParams *p)
>  {
>      MultiFDPages_t *pages = &p->data->u.ram;
> @@ -117,7 +124,7 @@ static int multifd_nocomp_send_prepare(MultiFDSendParams *p, Error **errp)
>           * Only !zerocopy needs the header in IOV; zerocopy will
>           * send it separately.
>           */
> -        multifd_send_prepare_header(p);
> +        multifd_ram_prepare_header(p);
>      }
>  
>      multifd_send_prepare_iovs(p);
> @@ -368,7 +375,7 @@ bool multifd_send_prepare_common(MultiFDSendParams *p)
>          return false;
>      }
>  
> -    multifd_send_prepare_header(p);
> +    multifd_ram_prepare_header(p);
>  
>      return true;
>  }
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 730acf55cfad..56419af417cc 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -12,6 +12,7 @@
>  
>  #include "qemu/osdep.h"
>  #include "qemu/cutils.h"
> +#include "qemu/iov.h"
>  #include "qemu/rcu.h"
>  #include "exec/target_page.h"
>  #include "sysemu/sysemu.h"
> @@ -19,6 +20,7 @@
>  #include "qemu/error-report.h"
>  #include "qapi/error.h"
>  #include "file.h"
> +#include "migration/misc.h"
>  #include "migration.h"
>  #include "migration-stats.h"
>  #include "savevm.h"
> @@ -111,7 +113,9 @@ MultiFDSendData *multifd_send_data_alloc(void)
>       * added to the union in the future are larger than
>       * (MultiFDPages_t + flex array).
>       */
> -    max_payload_size = MAX(multifd_ram_payload_size(), sizeof(MultiFDPayload));
> +    max_payload_size = MAX(multifd_ram_payload_size(),
> +                           multifd_device_state_payload_size());
> +    max_payload_size = MAX(max_payload_size, sizeof(MultiFDPayload));
>  
>      /*
>       * Account for any holes the compiler might insert. We can't pack
> @@ -130,6 +134,9 @@ void multifd_send_data_clear(MultiFDSendData *data)
>      }
>  
>      switch (data->type) {
> +    case MULTIFD_PAYLOAD_DEVICE_STATE:
> +        multifd_device_state_clear(&data->u.device_state);
> +        break;
>      default:
>          /* Nothing to do */
>          break;
> @@ -232,6 +239,7 @@ static int multifd_recv_initial_packet(QIOChannel *c, Error **errp)
>      return msg.id;
>  }
>  
> +/* Fills a RAM multifd packet */
>  void multifd_send_fill_packet(MultiFDSendParams *p)
>  {
>      MultiFDPacket_t *packet = p->packet;
> @@ -524,6 +532,7 @@ static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
>      p->name = NULL;
>      g_clear_pointer(&p->data, multifd_send_data_free);
>      p->packet_len = 0;
> +    g_clear_pointer(&p->packet_device_state, g_free);
>      g_free(p->packet);
>      p->packet = NULL;
>      multifd_send_state->ops->send_cleanup(p, errp);
> @@ -536,6 +545,7 @@ static void multifd_send_cleanup_state(void)
>  {
>      file_cleanup_outgoing_migration();
>      socket_cleanup_outgoing_migration();
> +    multifd_device_state_send_cleanup();
>      qemu_sem_destroy(&multifd_send_state->channels_created);
>      qemu_sem_destroy(&multifd_send_state->channels_ready);
>      qemu_mutex_destroy(&multifd_send_state->multifd_send_mutex);
> @@ -662,16 +672,33 @@ static void *multifd_send_thread(void *opaque)
>           * qatomic_store_release() in multifd_send().
>           */
>          if (qatomic_load_acquire(&p->pending_job)) {
> +            bool is_device_state = multifd_payload_device_state(p->data);
> +            size_t total_size;
> +
>              p->flags = 0;
>              p->iovs_num = 0;
>              assert(!multifd_payload_empty(p->data));
>  
> -            ret = multifd_send_state->ops->send_prepare(p, &local_err);
> -            if (ret != 0) {
> -                break;
> +            if (is_device_state) {
> +                multifd_device_state_send_prepare(p);
> +
> +                total_size = iov_size(p->iov, p->iovs_num);

This is such a good idea, because it allows us to kill
next_packet_size. Let's make it work.

What if you add packet_len to mig_stats under use_zero_copy at
multifd_nocomp_send_prepare? It's only fair since that's when the data
is actually sent. Then this total_size gets consolidated between the
paths.

> +            } else {
> +                ret = multifd_send_state->ops->send_prepare(p, &local_err);
> +                if (ret != 0) {
> +                    break;
> +                }
> +
> +                /*
> +                 * Can't just always measure IOVs since these do not include
> +                 * packet header in the zerocopy RAM case.
> +                 */
> +                total_size = (uint64_t)p->next_packet_size + p->packet_len;
>              }
>  
>              if (migrate_mapped_ram()) {
> +                assert(!is_device_state);
> +
>                  ret = file_write_ramblock_iov(p->c, p->iov, p->iovs_num,
>                                                &p->data->u.ram, &local_err);
>              } else {
> @@ -684,8 +711,7 @@ static void *multifd_send_thread(void *opaque)
>                  break;
>              }
>  
> -            stat64_add(&mig_stats.multifd_bytes,
> -                       (uint64_t)p->next_packet_size + p->packet_len);
> +            stat64_add(&mig_stats.multifd_bytes, total_size);
>  
>              p->next_packet_size = 0;
>              multifd_send_data_clear(p->data);
> @@ -903,6 +929,9 @@ bool multifd_send_setup(void)
>              p->packet_len = sizeof(MultiFDPacket_t)
>                            + sizeof(uint64_t) * page_count;
>              p->packet = g_malloc0(p->packet_len);
> +            p->packet_device_state = g_malloc0(sizeof(*p->packet_device_state));
> +            p->packet_device_state->hdr.magic = cpu_to_be32(MULTIFD_MAGIC);
> +            p->packet_device_state->hdr.version = cpu_to_be32(MULTIFD_VERSION);
>          }
>          p->name = g_strdup_printf(MIGRATION_THREAD_SRC_MULTIFD, i);
>          p->write_flags = 0;
> @@ -938,6 +967,8 @@ bool multifd_send_setup(void)
>          assert(p->iov);
>      }
>  
> +    multifd_device_state_send_setup();
> +
>      return true;
>  
>  err:
> diff --git a/migration/multifd.h b/migration/multifd.h
> index d2f1d0d74da7..dec7d9404434 100644
> --- a/migration/multifd.h
> +++ b/migration/multifd.h
> @@ -121,10 +121,12 @@ typedef struct {
>  typedef enum {
>      MULTIFD_PAYLOAD_NONE,
>      MULTIFD_PAYLOAD_RAM,
> +    MULTIFD_PAYLOAD_DEVICE_STATE,
>  } MultiFDPayloadType;
>  
>  typedef union MultiFDPayload {
>      MultiFDPages_t ram;
> +    MultiFDDeviceState_t device_state;
>  } MultiFDPayload;
>  
>  struct MultiFDSendData {
> @@ -137,6 +139,11 @@ static inline bool multifd_payload_empty(MultiFDSendData *data)
>      return data->type == MULTIFD_PAYLOAD_NONE;
>  }
>  
> +static inline bool multifd_payload_device_state(MultiFDSendData *data)
> +{
> +    return data->type == MULTIFD_PAYLOAD_DEVICE_STATE;
> +}
> +
>  static inline void multifd_set_payload_type(MultiFDSendData *data,
>                                              MultiFDPayloadType type)
>  {
> @@ -188,8 +195,9 @@ typedef struct {
>  
>      /* thread local variables. No locking required */
>  
> -    /* pointer to the packet */
> +    /* pointers to the possible packet types */
>      MultiFDPacket_t *packet;
> +    MultiFDPacketDeviceState_t *packet_device_state;
>      /* size of the next packet that contains pages */
>      uint32_t next_packet_size;
>      /* packets sent through this channel */
> @@ -346,13 +354,6 @@ bool multifd_send_prepare_common(MultiFDSendParams *p);
>  void multifd_send_zero_page_detect(MultiFDSendParams *p);
>  void multifd_recv_zero_page_process(MultiFDRecvParams *p);
>  
> -static inline void multifd_send_prepare_header(MultiFDSendParams *p)
> -{
> -    p->iov[0].iov_len = p->packet_len;
> -    p->iov[0].iov_base = p->packet;
> -    p->iovs_num++;
> -}
> -
>  void multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc);
>  bool multifd_send(MultiFDSendData **send_data);
>  MultiFDSendData *multifd_send_data_alloc(void);
> @@ -375,4 +376,11 @@ int multifd_ram_flush_and_sync(void);
>  size_t multifd_ram_payload_size(void);
>  void multifd_ram_fill_packet(MultiFDSendParams *p);
>  int multifd_ram_unfill_packet(MultiFDRecvParams *p, Error **errp);
> +
> +size_t multifd_device_state_payload_size(void);
> +void multifd_device_state_send_setup(void);
> +void multifd_device_state_clear(MultiFDDeviceState_t *device_state);
> +void multifd_device_state_send_cleanup(void);
> +void multifd_device_state_send_prepare(MultiFDSendParams *p);
> +
>  #endif