On Mon, Nov 27, 2023 at 05:25:53PM -0300, Fabiano Rosas wrote:
> For the upcoming support to the new 'fixed-ram' migration stream
> format, we cannot use multifd packets because each write into the
> ramblock section in the migration file is expected to contain only the
> guest pages. They are written at their respective offsets relative to
> the ramblock section header.
>
> There is no space for the packet information and the expected gains
> from the new approach come partly from being able to write the pages
> sequentially without extraneous data in between.
>
> The new format also doesn't need the packets and all necessary
> information can be taken from the standard migration headers with some
> (future) changes to multifd code.
>
> Use the presence of the fixed-ram capability to decide whether to send
> packets. For now this has no effect as fixed-ram cannot yet be enabled
> with multifd.
>
> Signed-off-by: Fabiano Rosas <[email protected]>
> ---
> - moved more of the packet code under use_packets
> ---
> migration/multifd.c | 138 +++++++++++++++++++++++++++-----------------
> migration/options.c | 5 ++
> migration/options.h | 1 +
> 3 files changed, 91 insertions(+), 53 deletions(-)
>
> diff --git a/migration/multifd.c b/migration/multifd.c
> index ec58c58082..9625640d61 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -654,18 +654,22 @@ static void *multifd_send_thread(void *opaque)
> Error *local_err = NULL;
> int ret = 0;
> bool use_zero_copy_send = migrate_zero_copy_send();
> + bool use_packets = migrate_multifd_packets();
>
> thread = migration_threads_add(p->name, qemu_get_thread_id());
>
> trace_multifd_send_thread_start(p->id);
> rcu_register_thread();
>
> - if (multifd_send_initial_packet(p, &local_err) < 0) {
> - ret = -1;
> - goto out;
> + if (use_packets) {
> + if (multifd_send_initial_packet(p, &local_err) < 0) {
> + ret = -1;
> + goto out;
> + }
> +
> + /* initial packet */
> + p->num_packets = 1;
> }
> - /* initial packet */
> - p->num_packets = 1;
>
> while (true) {
> qemu_sem_post(&multifd_send_state->channels_ready);
> @@ -677,11 +681,10 @@ static void *multifd_send_thread(void *opaque)
> qemu_mutex_lock(&p->mutex);
>
> if (p->pending_job) {
> - uint64_t packet_num = p->packet_num;
> uint32_t flags;
> p->normal_num = 0;
>
> - if (use_zero_copy_send) {
> + if (!use_packets || use_zero_copy_send) {
> p->iovs_num = 0;
> } else {
> p->iovs_num = 1;
> @@ -699,16 +702,20 @@ static void *multifd_send_thread(void *opaque)
> break;
> }
> }
> - multifd_send_fill_packet(p);
> +
> + if (use_packets) {
> + multifd_send_fill_packet(p);
> + p->num_packets++;
> + }
> +
> flags = p->flags;
> p->flags = 0;
> - p->num_packets++;
> p->total_normal_pages += p->normal_num;
> p->pages->num = 0;
> p->pages->block = NULL;
> qemu_mutex_unlock(&p->mutex);
>
> - trace_multifd_send(p->id, packet_num, p->normal_num, flags,
> + trace_multifd_send(p->id, p->packet_num, p->normal_num, flags,
> p->next_packet_size);
>
> if (use_zero_copy_send) {
> @@ -718,7 +725,7 @@ static void *multifd_send_thread(void *opaque)
> if (ret != 0) {
> break;
> }
> - } else {
> + } else if (use_packets) {
> /* Send header using the same writev call */
> p->iov[0].iov_len = p->packet_len;
> p->iov[0].iov_base = p->packet;
> @@ -904,6 +911,7 @@ int multifd_save_setup(Error **errp)
> {
> int thread_count;
> uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
> + bool use_packets = migrate_multifd_packets();
> uint8_t i;
>
> if (!migrate_multifd()) {
> @@ -928,14 +936,20 @@ int multifd_save_setup(Error **errp)
> p->pending_job = 0;
> p->id = i;
> p->pages = multifd_pages_init(page_count);
> - p->packet_len = sizeof(MultiFDPacket_t)
> - + sizeof(uint64_t) * page_count;
> - p->packet = g_malloc0(p->packet_len);
> - p->packet->magic = cpu_to_be32(MULTIFD_MAGIC);
> - p->packet->version = cpu_to_be32(MULTIFD_VERSION);
> +
> + if (use_packets) {
> + p->packet_len = sizeof(MultiFDPacket_t)
> + + sizeof(uint64_t) * page_count;
> + p->packet = g_malloc0(p->packet_len);
> + p->packet->magic = cpu_to_be32(MULTIFD_MAGIC);
> + p->packet->version = cpu_to_be32(MULTIFD_VERSION);
> +
> + /* We need one extra place for the packet header */
> + p->iov = g_new0(struct iovec, page_count + 1);
> + } else {
> + p->iov = g_new0(struct iovec, page_count);
> + }
> p->name = g_strdup_printf("multifdsend_%d", i);
> - /* We need one extra place for the packet header */
> - p->iov = g_new0(struct iovec, page_count + 1);
> p->normal = g_new0(ram_addr_t, page_count);
> p->page_size = qemu_target_page_size();
> p->page_count = page_count;
> @@ -1067,7 +1081,7 @@ void multifd_recv_sync_main(void)
> {
> int i;
>
> - if (!migrate_multifd()) {
> + if (!migrate_multifd() || !migrate_multifd_packets()) {
> return;
> }
> for (i = 0; i < migrate_multifd_channels(); i++) {
This noops the recv sync when use_packets=1, makes sense.
How about multifd_send_sync_main()? Should we do the same?
> @@ -1094,38 +1108,44 @@ static void *multifd_recv_thread(void *opaque)
> {
> MultiFDRecvParams *p = opaque;
> Error *local_err = NULL;
> + bool use_packets = migrate_multifd_packets();
> int ret;
>
> trace_multifd_recv_thread_start(p->id);
> rcu_register_thread();
>
> while (true) {
> - uint32_t flags;
> + uint32_t flags = 0;
> + p->normal_num = 0;
>
> if (p->quit) {
> break;
> }
>
> - ret = qio_channel_read_all_eof(p->c, (void *)p->packet,
> - p->packet_len, &local_err);
> - if (ret == 0 || ret == -1) { /* 0: EOF -1: Error */
> - break;
> - }
> + if (use_packets) {
> + ret = qio_channel_read_all_eof(p->c, (void *)p->packet,
> + p->packet_len, &local_err);
> + if (ret == 0 || ret == -1) { /* 0: EOF -1: Error */
> + break;
> + }
> +
> + qemu_mutex_lock(&p->mutex);
> + ret = multifd_recv_unfill_packet(p, &local_err);
> + if (ret) {
> + qemu_mutex_unlock(&p->mutex);
> + break;
> + }
> + p->num_packets++;
> +
> + flags = p->flags;
> + /* recv methods don't know how to handle the SYNC flag */
> + p->flags &= ~MULTIFD_FLAG_SYNC;
> + trace_multifd_recv(p->id, p->packet_num, p->normal_num, flags,
> + p->next_packet_size);
>
> - qemu_mutex_lock(&p->mutex);
> - ret = multifd_recv_unfill_packet(p, &local_err);
> - if (ret) {
> - qemu_mutex_unlock(&p->mutex);
> - break;
> + p->total_normal_pages += p->normal_num;
> }
>
> - flags = p->flags;
> - /* recv methods don't know how to handle the SYNC flag */
> - p->flags &= ~MULTIFD_FLAG_SYNC;
> - trace_multifd_recv(p->id, p->packet_num, p->normal_num, flags,
> - p->next_packet_size);
> - p->num_packets++;
> - p->total_normal_pages += p->normal_num;
> qemu_mutex_unlock(&p->mutex);
>
> if (p->normal_num) {
> @@ -1135,7 +1155,7 @@ static void *multifd_recv_thread(void *opaque)
> }
> }
>
> - if (flags & MULTIFD_FLAG_SYNC) {
> + if (use_packets && (flags & MULTIFD_FLAG_SYNC)) {
> qemu_sem_post(&multifd_recv_state->sem_sync);
> qemu_sem_wait(&p->sem_sync);
> }
> @@ -1159,6 +1179,7 @@ int multifd_load_setup(Error **errp)
> {
> int thread_count;
> uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
> + bool use_packets = migrate_multifd_packets();
> uint8_t i;
>
> /*
> @@ -1183,9 +1204,12 @@ int multifd_load_setup(Error **errp)
> qemu_sem_init(&p->sem_sync, 0);
> p->quit = false;
> p->id = i;
> - p->packet_len = sizeof(MultiFDPacket_t)
> - + sizeof(uint64_t) * page_count;
> - p->packet = g_malloc0(p->packet_len);
> +
> + if (use_packets) {
> + p->packet_len = sizeof(MultiFDPacket_t)
> + + sizeof(uint64_t) * page_count;
> + p->packet = g_malloc0(p->packet_len);
> + }
> p->name = g_strdup_printf("multifdrecv_%d", i);
> p->iov = g_new0(struct iovec, page_count);
> p->normal = g_new0(ram_addr_t, page_count);
> @@ -1231,18 +1255,27 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error
> **errp)
> {
> MultiFDRecvParams *p;
> Error *local_err = NULL;
> - int id;
> + bool use_packets = migrate_multifd_packets();
> + int id, num_packets = 0;
>
> - id = multifd_recv_initial_packet(ioc, &local_err);
> - if (id < 0) {
> - multifd_recv_terminate_threads(local_err);
> - error_propagate_prepend(errp, local_err,
> - "failed to receive packet"
> - " via multifd channel %d: ",
> - qatomic_read(&multifd_recv_state->count));
> - return;
> + if (use_packets) {
> + id = multifd_recv_initial_packet(ioc, &local_err);
> + if (id < 0) {
> + multifd_recv_terminate_threads(local_err);
> + error_propagate_prepend(errp, local_err,
> + "failed to receive packet"
> + " via multifd channel %d: ",
> +
> qatomic_read(&multifd_recv_state->count));
> + return;
> + }
> + trace_multifd_recv_new_channel(id);
> +
> + /* initial packet */
> + num_packets = 1;
> + } else {
> + /* next patch gives this a meaningful value */
> + id = 0;
> }
> - trace_multifd_recv_new_channel(id);
>
> p = &multifd_recv_state->params[id];
> if (p->c != NULL) {
> @@ -1253,9 +1286,8 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error
> **errp)
> return;
> }
> p->c = ioc;
> + p->num_packets = num_packets;
> object_ref(OBJECT(ioc));
> - /* initial packet */
> - p->num_packets = 1;
>
> p->running = true;
> qemu_thread_create(&p->thread, p->name, multifd_recv_thread, p,
> diff --git a/migration/options.c b/migration/options.c
> index 775428a8a5..10730b13ba 100644
> --- a/migration/options.c
> +++ b/migration/options.c
> @@ -385,6 +385,11 @@ bool migrate_multifd_flush_after_each_section(void)
> return s->multifd_flush_after_each_section;
> }
>
> +bool migrate_multifd_packets(void)
Maybe multifd_use_packets()? Dropping the migrate_ prefix as this is not a
global API but multifd-only. Then if multifd_packets() reads too weird and
unclear, "add" makes it clear.
> +{
> + return !migrate_fixed_ram();
> +}
> +
> bool migrate_postcopy(void)
> {
> return migrate_postcopy_ram() || migrate_dirty_bitmaps();
> diff --git a/migration/options.h b/migration/options.h
> index 8680a10b79..8a19d6939c 100644
> --- a/migration/options.h
> +++ b/migration/options.h
> @@ -56,6 +56,7 @@ bool migrate_zero_copy_send(void);
> */
>
> bool migrate_multifd_flush_after_each_section(void);
> +bool migrate_multifd_packets(void);
> bool migrate_postcopy(void);
> bool migrate_rdma(void);
> bool migrate_tls(void);
> --
> 2.35.3
>
--
Peter Xu
