On Wed, Feb 25, 2015 at 04:51:57PM +0000, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" > > When transmitting RAM pages, consume pages that have been queued by > MIG_RPCOMM_REQPAGE commands and send them ahead of normal page scanning. > > Note: > a) After a queued page the linear walk carries on from after the > unqueued page; there is a reasonable chance that the destination > was about to ask for other closeby pages anyway. > > b) We have to be careful of any assumptions that the page walking > code makes, in particular it does some short cuts on its first linear > walk that break as soon as we do a queued page. > > Signed-off-by: Dr. David Alan Gilbert > --- > arch_init.c | 154 +++++++++++++++++++++++++++++++++++++++++++++++++---------- > trace-events | 2 + > 2 files changed, 131 insertions(+), 25 deletions(-) > > diff --git a/arch_init.c b/arch_init.c > index 9d8fc6b..acf65e1 100644 > --- a/arch_init.c > +++ b/arch_init.c > @@ -328,6 +328,7 @@ static RAMBlock *last_seen_block; > /* This is the last block from where we have sent data */ > static RAMBlock *last_sent_block; > static ram_addr_t last_offset; > +static bool last_was_from_queue; > static unsigned long *migration_bitmap; > static uint64_t migration_dirty_pages; > static uint32_t last_version; > @@ -461,6 +462,19 @@ static inline bool migration_bitmap_set_dirty(ram_addr_t addr) > return ret; > } > > +static inline bool migration_bitmap_clear_dirty(ram_addr_t addr) > +{ > + bool ret; > + int nr = addr >> TARGET_PAGE_BITS; > + > + ret = test_and_clear_bit(nr, migration_bitmap); > + > + if (ret) { > + migration_dirty_pages--; > + } > + return ret; > +} > + > static void migration_bitmap_sync_range(ram_addr_t start, ram_addr_t length) > { > ram_addr_t addr; > @@ -669,6 +683,39 @@ static int ram_save_page(QEMUFile *f, RAMBlock* block, ram_addr_t offset, > } > > /* > + * Unqueue a page from the queue fed by postcopy page requests > + * > + * Returns: The RAMBlock* to transmit from (or NULL if the queue is empty) > + * ms: MigrationState in > + * offset: the byte offset within the RAMBlock for the start of the page > + * ram_addr_abs: global offset in the dirty/sent bitmaps > + */ > +static RAMBlock *ram_save_unqueue_page(MigrationState *ms, ram_addr_t *offset, > + ram_addr_t *ram_addr_abs) > +{ > + RAMBlock *result = NULL; > + qemu_mutex_lock(&ms->src_page_req_mutex); > + if (!QSIMPLEQ_EMPTY(&ms->src_page_requests)) { > + struct MigrationSrcPageRequest *entry = > + QSIMPLEQ_FIRST(&ms->src_page_requests); > + result = entry->rb; > + *offset = entry->offset; > + *ram_addr_abs = (entry->offset + entry->rb->offset) & TARGET_PAGE_MASK; > + > + if (entry->len > TARGET_PAGE_SIZE) { > + entry->len -= TARGET_PAGE_SIZE; > + entry->offset += TARGET_PAGE_SIZE; > + } else { > + QSIMPLEQ_REMOVE_HEAD(&ms->src_page_requests, next_req); > + g_free(entry); > + } > + } > + qemu_mutex_unlock(&ms->src_page_req_mutex); > + > + return result; > +} > + > +/* > * Queue the pages for transmission, e.g. a request from postcopy destination > * ms: MigrationStatus in which the queue is held > * rbname: The RAMBlock the request is for - may be NULL (to mean reuse last) > @@ -732,46 +779,102 @@ int ram_save_queue_pages(MigrationState *ms, const char *rbname, > > static int ram_find_and_save_block(QEMUFile *f, bool last_stage) > { > + MigrationState *ms = migrate_get_current(); > RAMBlock *block = last_seen_block; > + RAMBlock *tmpblock; > ram_addr_t offset = last_offset; > + ram_addr_t tmpoffset; > bool complete_round = false; > int bytes_sent = 0; > - MemoryRegion *mr; > ram_addr_t dirty_ram_abs; /* Address of the start of the dirty page in > ram_addr_t space */ > + unsigned long hps = sysconf(_SC_PAGESIZE); > > - if (!block) > + if (!block) { > block = QTAILQ_FIRST(&ram_list.blocks); > + last_was_from_queue = false; > + } > > - while (true) { > - mr = block->mr; > - offset = migration_bitmap_find_and_reset_dirty(mr, offset, > - &dirty_ram_abs); > - if (complete_round && block == last_seen_block && > - offset >= last_offset) { > - break; > + while (true) { /* Until we send a block or run out of stuff to send */ > + tmpblock = NULL; > + > + /* > + * Don't break host-page chunks up with queue items > + * so only unqueue if, > + * a) The last item came from the queue anyway > + * b) The last sent item was the last target-page in a host page > + */ > + if (last_was_from_queue || !last_sent_block || > + ((last_offset & (hps - 1)) == (hps - TARGET_PAGE_SIZE))) { > + tmpblock = ram_save_unqueue_page(ms, &tmpoffset, &dirty_ram_abs); This test for whether we've completed a host page is pretty awkward. I think it would be cleaner to have an inner loop / helper function that completes sending an entire host page (whether requested or scanned), before allowing the outer loop to even come back to here to reconsider the queue. > } > - if (offset >= block->used_length) { > - offset = 0; > - block = QTAILQ_NEXT(block, next); > - if (!block) { > - block = QTAILQ_FIRST(&ram_list.blocks); > - complete_round = true; > - ram_bulk_stage = false; > + > + if (tmpblock) { > + /* We've got a block from the postcopy queue */ > + trace_ram_find_and_save_block_postcopy(tmpblock->idstr, > + (uint64_t)tmpoffset, > + (uint64_t)dirty_ram_abs); > + /* > + * We're sending this page, and since it's postcopy nothing else > + * will dirty it, and we must make sure it doesn't get sent again. > + */ > + if (!migration_bitmap_clear_dirty(dirty_ram_abs)) { > + trace_ram_find_and_save_block_postcopy_not_dirty( > + tmpblock->idstr, (uint64_t)tmpoffset, > + (uint64_t)dirty_ram_abs, > + test_bit(dirty_ram_abs >> TARGET_PAGE_BITS, ms->sentmap)); > + > + continue; > } > + /* > + * As soon as we start servicing pages out of order, then we have > + * to kill the bulk stage, since the bulk stage assumes > + * in (migration_bitmap_find_and_reset_dirty) that every page is > + * dirty, that's no longer true. > + */ > + ram_bulk_stage = false; > + /* > + * We mustn't change block/offset unless it's to a valid one > + * otherwise we can go down some of the exit cases in the normal > + * path. > + */ > + block = tmpblock; > + offset = tmpoffset; > + last_was_from_queue = true; Hrm. So now block can change during the execution of ram_save_block(), which really suggests that splitting by block is no longer a sensible subdivision of the loop surrounding ram_save_block. I think it would make more sense to replace that entire surrounding loop, so that the logic is essentially while (not finished) { if (something is queued) { send that } else { scan for an unsent block and offset send that instead } > } else { > - bytes_sent = ram_save_page(f, block, offset, last_stage); > - > - /* if page is unmodified, continue to the next */ > - if (bytes_sent > 0) { > - MigrationState *ms = migrate_get_current(); > - if (ms->sentmap) { > - set_bit(dirty_ram_abs >> TARGET_PAGE_BITS, ms->sentmap); > + MemoryRegion *mr; > + /* priority queue empty, so just search for something dirty */ > + mr = block->mr; > + offset = migration_bitmap_find_and_reset_dirty(mr, offset, > + &dirty_ram_abs); > + if (complete_round && block == last_seen_block && > + offset >= last_offset) { > + break; > + } > + if (offset >= block->used_length) { > + offset = 0; > + block = QTAILQ_NEXT(block, next); > + if (!block) { > + block = QTAILQ_FIRST(&ram_list.blocks); > + complete_round = true; > + ram_bulk_stage = false; > } > + continue; /* pick an offset in the new block */ > + } > + last_was_from_queue = false; > + } > > - last_sent_block = block; > - break; > + /* We have a page to send, so send it */ > + bytes_sent = ram_save_page(f, block, offset, last_stage); > + > + /* if page is unmodified, continue to the next */ > + if (bytes_sent > 0) { > + if (ms->sentmap) { > + set_bit(dirty_ram_abs >> TARGET_PAGE_BITS, ms->sentmap); > } > + > + last_sent_block = block; > + break; > } > } > last_seen_block = block; > @@ -865,6 +968,7 @@ static void reset_ram_globals(void) > last_offset = 0; > last_version = ram_list.version; > ram_bulk_stage = true; > + last_was_from_queue = false; > } > > #define MAX_WAIT 50 /* ms, half buffered_file limit */ > diff --git a/trace-events b/trace-events > index 8a0d70d..781cf5c 100644 > --- a/trace-events > +++ b/trace-events > @@ -1217,6 +1217,8 @@ qemu_file_fclose(void) "" > migration_bitmap_sync_start(void) "" > migration_bitmap_sync_end(uint64_t dirty_pages) "dirty_pages %" PRIu64"" > migration_throttle(void) "" > +ram_find_and_save_block_postcopy(const char *block_name, uint64_t tmp_offset, uint64_t ram_addr) "%s/%" PRIx64 " ram_addr=%" PRIx64 > +ram_find_and_save_block_postcopy_not_dirty(const char *block_name, uint64_t tmp_offset, uint64_t ram_addr, int sent) "%s/%" PRIx64 " ram_addr=%" PRIx64 " (sent=%d)" > ram_postcopy_send_discard_bitmap(void) "" > ram_save_queue_pages(const char *rbname, size_t start, size_t len) "%s: start: %zx len: %zx" > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson