On Fri, Oct 03, 2014 at 06:47:43PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
>
> 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 <dgilb...@redhat.com>
> ---
> arch_init.c | 149
> ++++++++++++++++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 125 insertions(+), 24 deletions(-)
>
> diff --git a/arch_init.c b/arch_init.c
> index 72f9e17..a945990 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -331,6 +331,7 @@ 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;
> @@ -460,6 +461,19 @@ 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;
> @@ -660,6 +674,39 @@ 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
> + * bitoffset: global offset in the dirty/sent bitmaps
> + */
> +static RAMBlock *ram_save_unqueue_page(MigrationState *ms, ram_addr_t
> *offset,
> + unsigned long *bitoffset)
> +{
> + 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;
> + *bitoffset = (entry->offset + entry->rb->offset) >> TARGET_PAGE_BITS;
> +
> + 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)
> @@ -720,44 +767,97 @@ 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;
> unsigned long bitoffset;
> + 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,
> &bitoffset);
> - 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
Why does this matter?
> + * 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, &bitoffset);
> }
> - if (offset >= block->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 */
> + DPRINTF("%s: Got postcopy item '%s' offset=%zx bitoffset=%zx",
> + __func__, tmpblock->idstr, tmpoffset, bitoffset);
> + /* 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(bitoffset <<
> TARGET_PAGE_BITS)) {
Ugh.. that's kind of subtle. I think it would be clearer if you work
in terms of a ram_addr_t throughout, rather than "bitoffset" whose
meaning is not terribly obvious.
--
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
pgp6WJkRbDnAN.pgp
Description: PGP signature
