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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: Peter Xu <peterx@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com>
Message-Id: <20180903092644.25812-3-xiaoguangrong@tencent.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Xiao Guangrong 2018-09-03 17:26:42 +08:00 committed by Dr. David Alan Gilbert
parent 449f91b2c8
commit be8b02edae
1 changed files with 9 additions and 9 deletions
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18
migration/ram.c
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@ -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.