On Mon, Jul 17, 2017 at 03:42:38PM +0200, Juan Quintela wrote:
> Each time that we sync the bitmap, it is a possiblity that we receive
> a page that is being processed by a different thread. We fix this
> problem just making sure that we wait for all receiving threads to
> finish its work before we procedeed with the next stage.
>
> We are low on page flags, so we use a combination that is not valid to
> emit that message: MULTIFD_PAGE and COMPRESSED.
>
> I tried to make a migration command for it, but it don't work because
> we sync the bitmap sometimes when we have already sent the beggining
> of the section, so I just added a new page flag.
>
> Signed-off-by: Juan Quintela <quint...@redhat.com>
> ---
> migration/ram.c | 57
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 56 insertions(+), 1 deletion(-)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index c78b286..bffe204 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -71,6 +71,12 @@
> #define RAM_SAVE_FLAG_COMPRESS_PAGE 0x100
> #define RAM_SAVE_FLAG_MULTIFD_PAGE 0x200
>
> +/* We are getting low on pages flags, so we start using combinations
> + When we need to flush a page, we sent it as
> + RAM_SAVE_FLAG_MULTIFD_PAGE | RAM_SAVE_FLAG_COMPRESS_PAGE
> + We don't allow that combination
> +*/
> +
> static inline bool is_zero_range(uint8_t *p, uint64_t size)
> {
> return buffer_is_zero(p, size);
> @@ -193,6 +199,9 @@ struct RAMState {
> uint64_t iterations_prev;
> /* Iterations since start */
> uint64_t iterations;
> + /* Indicates if we have synced the bitmap and we need to assure that
> + target has processeed all previous pages */
> + bool multifd_needs_flush;
> /* protects modification of the bitmap */
> uint64_t migration_dirty_pages;
> /* number of dirty bits in the bitmap */
> @@ -363,7 +372,6 @@ static void compress_threads_save_setup(void)
>
> /* Multiple fd's */
>
> -
> typedef struct {
> int num;
> int size;
> @@ -595,9 +603,11 @@ struct MultiFDRecvParams {
> QIOChannel *c;
> QemuSemaphore ready;
> QemuSemaphore sem;
> + QemuCond cond_sync;
> QemuMutex mutex;
> /* proteced by param mutex */
> bool quit;
> + bool sync;
> multifd_pages_t pages;
> bool done;
> };
> @@ -637,6 +647,7 @@ void multifd_load_cleanup(void)
> qemu_thread_join(&p->thread);
> qemu_mutex_destroy(&p->mutex);
> qemu_sem_destroy(&p->sem);
> + qemu_cond_destroy(&p->cond_sync);
> socket_recv_channel_destroy(p->c);
> g_free(p);
> multifd_recv_state->params[i] = NULL;
> @@ -675,6 +686,10 @@ static void *multifd_recv_thread(void *opaque)
> return NULL;
> }
> p->done = true;
> + if (p->sync) {
> + qemu_cond_signal(&p->cond_sync);
> + p->sync = false;
> + }
Could we use the same p->ready for this purpose? They looks similar:
all we want to do is to let the main thread know "worker thread has
finished receiving the last piece and becomes idle again", right?
> qemu_mutex_unlock(&p->mutex);
> qemu_sem_post(&p->ready);
> continue;
> @@ -724,9 +739,11 @@ gboolean multifd_new_channel(QIOChannel *ioc)
> qemu_mutex_init(&p->mutex);
> qemu_sem_init(&p->sem, 0);
> qemu_sem_init(&p->ready, 0);
> + qemu_cond_init(&p->cond_sync);
> p->quit = false;
> p->id = id;
> p->done = false;
> + p->sync = false;
> multifd_init_group(&p->pages);
> p->c = ioc;
> atomic_set(&multifd_recv_state->params[id], p);
> @@ -792,6 +809,27 @@ static void multifd_recv_page(uint8_t *address, uint16_t
> fd_num)
> qemu_sem_post(&p->sem);
> }
>
> +static int multifd_flush(void)
> +{
> + int i, thread_count;
> +
> + if (!migrate_use_multifd()) {
> + return 0;
> + }
> + thread_count = migrate_multifd_threads();
> + for (i = 0; i < thread_count; i++) {
> + MultiFDRecvParams *p = multifd_recv_state->params[i];
> +
> + qemu_mutex_lock(&p->mutex);
> + while (!p->done) {
> + p->sync = true;
> + qemu_cond_wait(&p->cond_sync, &p->mutex);
(similar comment like above)
> + }
> + qemu_mutex_unlock(&p->mutex);
> + }
> + return 0;
> +}
> +
> /**
> * save_page_header: write page header to wire
> *
> @@ -809,6 +847,12 @@ static size_t save_page_header(RAMState *rs, QEMUFile
> *f, RAMBlock *block,
> {
> size_t size, len;
>
> + if (rs->multifd_needs_flush &&
> + (offset & RAM_SAVE_FLAG_MULTIFD_PAGE)) {
If multifd_needs_flush is only for multifd, then we may skip this
check, but it looks more like an assertion:
if (rs->multifd_needs_flush) {
assert(offset & RAM_SAVE_FLAG_MULTIFD_PAGE);
offset |= RAM_SAVE_FLAG_ZERO;
}
(Dave mentioned about unaligned flag used in commit message and here:
ZERO is used, but COMPRESS is mentioned)
> + offset |= RAM_SAVE_FLAG_ZERO;
> + rs->multifd_needs_flush = false;
> + }
> +
> if (block == rs->last_sent_block) {
> offset |= RAM_SAVE_FLAG_CONTINUE;
> }
> @@ -2496,6 +2540,9 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
>
> if (!migration_in_postcopy()) {
> migration_bitmap_sync(rs);
> + if (migrate_use_multifd()) {
> + rs->multifd_needs_flush = true;
> + }
Would it be good to move this block into entry of
migration_bitmap_sync(), instead of setting it up at the callers of
migration_bitmap_sync()?
> }
>
> ram_control_before_iterate(f, RAM_CONTROL_FINISH);
> @@ -2538,6 +2585,9 @@ static void ram_save_pending(QEMUFile *f, void *opaque,
> uint64_t max_size,
> qemu_mutex_lock_iothread();
> rcu_read_lock();
> migration_bitmap_sync(rs);
> + if (migrate_use_multifd()) {
> + rs->multifd_needs_flush = true;
> + }
> rcu_read_unlock();
> qemu_mutex_unlock_iothread();
> remaining_size = rs->migration_dirty_pages * TARGET_PAGE_SIZE;
> @@ -3012,6 +3062,11 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> break;
> }
>
> + if ((flags & (RAM_SAVE_FLAG_MULTIFD_PAGE | RAM_SAVE_FLAG_ZERO))
> + == (RAM_SAVE_FLAG_MULTIFD_PAGE | RAM_SAVE_FLAG_ZERO)) {
> + multifd_flush();
> + flags = flags & ~RAM_SAVE_FLAG_ZERO;
> + }
> if (flags & (RAM_SAVE_FLAG_ZERO | RAM_SAVE_FLAG_PAGE |
> RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE |
> RAM_SAVE_FLAG_MULTIFD_PAGE)) {
> --
> 2.9.4
>
Thanks,
--
Peter Xu
