On Fri, Sep 22, 2017 at 12:33:19PM +0100, Dr. David Alan Gilbert wrote:
> * 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.
This is to note when we start to wait, while there is a trace below
when we reload one single ramblock at [1]. Would that suffice?
>
> > +
> > + /* 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....
You are right!
>
> > +
> > + 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.
Yes. I'll also remove the notify trace since there is a better
tracepoint before calling this function.
>
> > +}
> > +
> > /*
> > * 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);
[1]
> >
> > + /*
> > + * 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
--
Peter Xu
