* Peter Xu (pet...@redhat.com) wrote:
> This patch implements the first part of core RAM resume logic for
> postcopy. ram_resume_prepare() is provided for the work.
>
> When the migration is interrupted by network failure, the dirty bitmap
> on the source side will be meaningless, because even the dirty bit is
> cleared, it is still possible that the sent page was lost along the way
> to destination. Here instead of continue the migration with the old
> dirty bitmap on source, we ask the destination side to send back its
> received bitmap, then invert it to be our initial dirty bitmap.
>
> The source side send thread will issue the MIG_CMD_RECV_BITMAP requests,
> once per ramblock, to ask for the received bitmap. On destination side,
> MIG_RP_MSG_RECV_BITMAP will be issued, along with the requested bitmap.
> Data will be received on the return-path thread of source, and the main
> migration thread will be notified when all the ramblock bitmaps are
> synchronized.
>
> Signed-off-by: Peter Xu <pet...@redhat.com>
> ---
> migration/migration.c | 4 +++
> migration/migration.h | 1 +
> migration/ram.c | 67
> ++++++++++++++++++++++++++++++++++++++++++++++++++
> migration/trace-events | 4 +++
> 4 files changed, 76 insertions(+)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index 19b7f3a5..19aed72 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -2605,6 +2605,8 @@ static void migration_instance_finalize(Object *obj)
>
> g_free(params->tls_hostname);
> g_free(params->tls_creds);
> +
> + qemu_sem_destroy(&ms->rp_state.rp_sem);
> }
>
> static void migration_instance_init(Object *obj)
> @@ -2629,6 +2631,8 @@ static void migration_instance_init(Object *obj)
> params->has_downtime_limit = true;
> params->has_x_checkpoint_delay = true;
> params->has_block_incremental = true;
> +
> + qemu_sem_init(&ms->rp_state.rp_sem, 1);
> }
>
> /*
> diff --git a/migration/migration.h b/migration/migration.h
> index a3a0582..d041369 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -107,6 +107,7 @@ struct MigrationState
> QEMUFile *from_dst_file;
> QemuThread rp_thread;
> bool error;
> + QemuSemaphore rp_sem;
> } rp_state;
>
> double mbps;
> diff --git a/migration/ram.c b/migration/ram.c
> index 5d938e3..afabcf5 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -47,6 +47,7 @@
> #include "exec/target_page.h"
> #include "qemu/rcu_queue.h"
> #include "migration/colo.h"
> +#include "savevm.h"
>
> /***********************************************************/
> /* ram save/restore */
> @@ -295,6 +296,8 @@ struct RAMState {
> RAMBlock *last_req_rb;
> /* Queue of outstanding page requests from the destination */
> QemuMutex src_page_req_mutex;
> + /* Ramblock counts to sync dirty bitmap. Only used for recovery */
> + int ramblock_to_sync;
> QSIMPLEQ_HEAD(src_page_requests, RAMSrcPageRequest) src_page_requests;
> };
> typedef struct RAMState RAMState;
> @@ -2770,6 +2773,56 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> return ret;
> }
>
> +/* Sync all the dirty bitmap with destination VM. */
> +static int ram_dirty_bitmap_sync_all(MigrationState *s, RAMState *rs)
> +{
> + RAMBlock *block;
> + QEMUFile *file = s->to_dst_file;
> + int ramblock_count = 0;
> +
> + trace_ram_dirty_bitmap_sync_start();
> +
> + /*
> + * We do this in such order:
> + *
> + * 1. calculate block count
> + * 2. fill in the count to N
> + * 3. send MIG_CMD_RECV_BITMAP requests
> + * 4. wait on the semaphore until N -> 0
> + */
> +
> + RAMBLOCK_FOREACH(block) {
> + ramblock_count++;
> + }
> +
> + atomic_set(&rs->ramblock_to_sync, ramblock_count);
> + RAMBLOCK_FOREACH(block) {
> + qemu_savevm_send_recv_bitmap(file, block->idstr);
> + }
> +
> + trace_ram_dirty_bitmap_sync_wait();
Please include the RAMBlock name in the trace, so if it hangs we can
see where.
> +
> + /* Wait until all the ramblocks' dirty bitmap synced */
> + while (atomic_read(&rs->ramblock_to_sync)) {
> + qemu_sem_wait(&s->rp_state.rp_sem);
> + }
Do you need to make ramblock_to_sync global and use atomics - I think
you can simplify it; if you qemu_sem_init to 0, then I think you
can do:
while (ramblock_count--) {
qemu_sem_wait(&s->rp_state.rp_sem);
}
qemu_sem_wait will block until the semaphore is >0....
> +
> + trace_ram_dirty_bitmap_sync_complete();
> +
> + return 0;
> +}
> +
> +static void ram_dirty_bitmap_reload_notify(MigrationState *s)
> +{
> + atomic_dec(&ram_state->ramblock_to_sync);
> + if (ram_state->ramblock_to_sync == 0) {
> + /* Make sure the other thread gets the latest */
> + trace_ram_dirty_bitmap_sync_notify();
> + qemu_sem_post(&s->rp_state.rp_sem);
> + }
then with the suggestion above you just do a qemu_sem_post each time.
> +}
> +
> /*
> * Read the received bitmap, revert it as the initial dirty bitmap.
> * This is only used when the postcopy migration is paused but wants
> @@ -2841,12 +2894,25 @@ int ram_dirty_bitmap_reload(MigrationState *s,
> RAMBlock *block)
>
> trace_ram_dirty_bitmap_reload(block->idstr);
>
> + /*
> + * We succeeded to sync bitmap for current ramblock. If this is
> + * the last one to sync, we need to notify the main send thread.
> + */
> + ram_dirty_bitmap_reload_notify(s);
> +
> ret = 0;
> out:
> free(le_bitmap);
> return ret;
> }
>
> +static int ram_resume_prepare(MigrationState *s, void *opaque)
> +{
> + RAMState *rs = *(RAMState **)opaque;
> +
> + return ram_dirty_bitmap_sync_all(s, rs);
> +}
> +
> static SaveVMHandlers savevm_ram_handlers = {
> .save_setup = ram_save_setup,
> .save_live_iterate = ram_save_iterate,
> @@ -2857,6 +2923,7 @@ static SaveVMHandlers savevm_ram_handlers = {
> .save_cleanup = ram_save_cleanup,
> .load_setup = ram_load_setup,
> .load_cleanup = ram_load_cleanup,
> + .resume_prepare = ram_resume_prepare,
> };
>
> void ram_mig_init(void)
> diff --git a/migration/trace-events b/migration/trace-events
> index 61b0d49..8962916 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -81,6 +81,10 @@ ram_postcopy_send_discard_bitmap(void) ""
> ram_save_page(const char *rbname, uint64_t offset, void *host) "%s: offset:
> 0x%" PRIx64 " host: %p"
> ram_save_queue_pages(const char *rbname, size_t start, size_t len) "%s:
> start: 0x%zx len: 0x%zx"
> ram_dirty_bitmap_reload(char *str) "%s"
> +ram_dirty_bitmap_sync_start(void) ""
> +ram_dirty_bitmap_sync_wait(void) ""
> +ram_dirty_bitmap_sync_notify(void) ""
> +ram_dirty_bitmap_sync_complete(void) ""
>
> # migration/migration.c
> await_return_path_close_on_source_close(void) ""
> --
> 2.7.4
>
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
