On 08/08/2018 02:05 PM, Peter Xu wrote:
On Tue, Aug 07, 2018 at 05:12:08PM +0800, guangrong.xiao@xxxxxxxxx wrote:
From: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxx>
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 guest page numbers
After that, rename 'iterations' to 'handle_pages' to better reflect
its meaning
Suggested-by: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxx>
---
migration/ram.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/migration/ram.c b/migration/ram.c
index 09be01dca2..bd7c18d1f9 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -300,10 +300,10 @@ 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 pages at the beginning of period */
+ uint64_t handle_pages_prev;
+ /* total handled pages since start */
+ uint64_t handle_pages;
The name is not that straightforward to me. I would think about
"[guest|host]_page_count" or something better, or we just keep the old
naming but with a better comment would be fine too.
The filed actually indicates total pages (target pages more precisely)
handled during live migration. 'iterations' confuses us completely.
It's target_page_count good to you?
/* number of dirty bits in the bitmap */
uint64_t migration_dirty_pages;
/* last dirty_sync_count we have seen */
@@ -1587,19 +1587,19 @@ 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->handle_pages - rs->handle_pages_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;
}
}
@@ -1657,7 +1657,7 @@ static void migration_bitmap_sync(RAMState *rs)
migration_update_rates(rs, end_time);
- rs->iterations_prev = rs->iterations;
+ rs->handle_pages_prev = rs->handle_pages;
/* reset period counters */
rs->time_last_bitmap_sync = end_time;
@@ -3209,7 +3209,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
break;
}
- rs->iterations++;
+ rs->handle_pages += pages;
So it's still counting host pages, is this your intention to only
change the name in the patch?
Hmm... the value returned by ram_find_and_save_block() isn't the total
target pages posted out?
/**
* ram_find_and_save_block: finds a dirty page and sends it to f
*
* Called within an RCU critical section.
*
* Returns the number of pages written where zero means no dirty pages,
* or negative on error
...
*
* On systems where host-page-size > target-page-size it will send all the
* pages in a host page that are dirty.
*/
