Commit be8b02ed authored by Xiao Guangrong's avatar Xiao Guangrong Committed by Dr. David Alan Gilbert
Browse files

migration: fix calculating xbzrle_counters.cache_miss_rate 



As Peter pointed out:
| - xbzrle_counters.cache_miss is done in save_xbzrle_page(), so it's
|   per-guest-page granularity
|
| - RAMState.iterations is done for each ram_find_and_save_block(), so
|   it's per-host-page granularity
|
| An example is that when we migrate a 2M huge page in the guest, we
| will only increase the RAMState.iterations by 1 (since
| ram_find_and_save_block() will be called once), but we might increase
| xbzrle_counters.cache_miss for 2M/4K=512 times (we'll call
| save_xbzrle_page() that many times) if all the pages got cache miss.
| Then IMHO the cache miss rate will be 512/1=51200% (while it should
| actually be just 100% cache miss).

And he also suggested as xbzrle_counters.cache_miss_rate is the only
user of rs->iterations we can adapt it to count target guest page
numbers

After that, rename 'iterations' to 'target_page_count' to better reflect
its meaning

Suggested-by: default avatarPeter Xu <peterx@redhat.com>
Reviewed-by: default avatarPeter Xu <peterx@redhat.com>
Reviewed-by: default avatarJuan Quintela <quintela@redhat.com>
Signed-off-by: default avatarXiao Guangrong <xiaoguangrong@tencent.com>
Message-Id: <20180903092644.25812-3-xiaoguangrong@tencent.com>
Signed-off-by: default avatarJuan Quintela <quintela@redhat.com>
Signed-off-by: default avatarDr. David Alan Gilbert <dgilbert@redhat.com>
parent 449f91b2

migration/ram.c

+9 −9
Original line number Diff line number Diff line
@@ -301,10 +301,10 @@ struct RAMState { 
    uint64_t num_dirty_pages_period;

    /* xbzrle misses since the beginning of the period */

    uint64_t xbzrle_cache_miss_prev;

    /* number of iterations at the beginning of period */

    uint64_t iterations_prev;

    /* Iterations since start */

    uint64_t iterations;

    /* total handled target pages at the beginning of period */

    uint64_t target_page_count_prev;

    /* total handled target pages since start */

    uint64_t target_page_count;

    /* number of dirty bits in the bitmap */

    uint64_t migration_dirty_pages;

    /* protects modification of the bitmap */
@@ -1592,19 +1592,19 @@ uint64_t ram_pagesize_summary(void) 


static void migration_update_rates(RAMState *rs, int64_t end_time)

{

    uint64_t iter_count = rs->iterations - rs->iterations_prev;

    uint64_t page_count = rs->target_page_count - rs->target_page_count_prev;



    /* calculate period counters */

    ram_counters.dirty_pages_rate = rs->num_dirty_pages_period * 1000

                / (end_time - rs->time_last_bitmap_sync);



    if (!iter_count) {

    if (!page_count) {

        return;

    }



    if (migrate_use_xbzrle()) {

        xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss -

            rs->xbzrle_cache_miss_prev) / iter_count;

            rs->xbzrle_cache_miss_prev) / page_count;

        rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss;

    }

}
@@ -1662,7 +1662,7 @@ static void migration_bitmap_sync(RAMState *rs) 


        migration_update_rates(rs, end_time);



        rs->iterations_prev = rs->iterations;

        rs->target_page_count_prev = rs->target_page_count;



        /* reset period counters */

        rs->time_last_bitmap_sync = end_time;
@@ -3196,7 +3196,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque) 
            done = 1;

            break;

        }

        rs->iterations++;

        rs->target_page_count += pages;



        /* we want to check in the 1st loop, just in case it was the 1st time

           and we had to sync the dirty bitmap.