diff options
| -rw-r--r-- | arch_init.c | 8 | ||||
| -rw-r--r-- | docs/xbzrle.txt | 8 | ||||
| -rw-r--r-- | include/migration/page_cache.h | 10 | ||||
| -rw-r--r-- | page_cache.c | 23 |
4 files changed, 39 insertions, 10 deletions
diff --git a/arch_init.c b/arch_init.c index cfedbf08af..89c8fa46bb 100644 --- a/arch_init.c +++ b/arch_init.c @@ -346,7 +346,8 @@ static void xbzrle_cache_zero_page(ram_addr_t current_addr) /* We don't care if this fails to allocate a new cache page * as long as it updated an old one */ - cache_insert(XBZRLE.cache, current_addr, ZERO_TARGET_PAGE); + cache_insert(XBZRLE.cache, current_addr, ZERO_TARGET_PAGE, + bitmap_sync_count); } #define ENCODING_FLAG_XBZRLE 0x1 @@ -358,10 +359,11 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t **current_data, int encoded_len = 0, bytes_sent = -1; uint8_t *prev_cached_page; - if (!cache_is_cached(XBZRLE.cache, current_addr)) { + if (!cache_is_cached(XBZRLE.cache, current_addr, bitmap_sync_count)) { acct_info.xbzrle_cache_miss++; if (!last_stage) { - if (cache_insert(XBZRLE.cache, current_addr, *current_data) == -1) { + if (cache_insert(XBZRLE.cache, current_addr, *current_data, + bitmap_sync_count) == -1) { return -1; } else { /* update *current_data when the page has been diff --git a/docs/xbzrle.txt b/docs/xbzrle.txt index cc3a26a91d..52c8511a4c 100644 --- a/docs/xbzrle.txt +++ b/docs/xbzrle.txt @@ -71,6 +71,14 @@ encoded buffer: encoded length 24 e9 07 0f 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 03 01 67 01 01 69 +Cache update strategy +===================== +Keeping the hot pages in the cache is effective for decreased cache +misses. XBZRLE uses a counter as the age of each page. The counter will +increase after each ram dirty bitmap sync. When a cache conflict is +detected, XBZRLE will only evict pages in the cache that are older than +a threshold. + Usage ====================== 1. Verify the destination QEMU version is able to decode the new format. diff --git a/include/migration/page_cache.h b/include/migration/page_cache.h index 2d5ce2dd7a..10ed53274c 100644 --- a/include/migration/page_cache.h +++ b/include/migration/page_cache.h @@ -43,8 +43,10 @@ void cache_fini(PageCache *cache); * * @cache pointer to the PageCache struct * @addr: page addr + * @current_age: current bitmap generation */ -bool cache_is_cached(const PageCache *cache, uint64_t addr); +bool cache_is_cached(const PageCache *cache, uint64_t addr, + uint64_t current_age); /** * get_cached_data: Get the data cached for an addr @@ -60,13 +62,15 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t addr); * cache_insert: insert the page into the cache. the page cache * will dup the data on insert. the previous value will be overwritten * - * Returns -1 on error + * Returns -1 when the page isn't inserted into cache * * @cache pointer to the PageCache struct * @addr: page address * @pdata: pointer to the page + * @current_age: current bitmap generation */ -int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata); +int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata, + uint64_t current_age); /** * cache_resize: resize the page cache. In case of size reduction the extra diff --git a/page_cache.c b/page_cache.c index 89bb1ec3a0..aa681923c6 100644 --- a/page_cache.c +++ b/page_cache.c @@ -33,6 +33,9 @@ do { } while (0) #endif +/* the page in cache will not be replaced in two cycles */ +#define CACHED_PAGE_LIFETIME 2 + typedef struct CacheItem CacheItem; struct CacheItem { @@ -122,7 +125,8 @@ static size_t cache_get_cache_pos(const PageCache *cache, return pos; } -bool cache_is_cached(const PageCache *cache, uint64_t addr) +bool cache_is_cached(const PageCache *cache, uint64_t addr, + uint64_t current_age) { size_t pos; @@ -131,7 +135,12 @@ bool cache_is_cached(const PageCache *cache, uint64_t addr) pos = cache_get_cache_pos(cache, addr); - return (cache->page_cache[pos].it_addr == addr); + if (cache->page_cache[pos].it_addr == addr) { + /* update the it_age when the cache hit */ + cache->page_cache[pos].it_age = current_age; + return true; + } + return false; } static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr) @@ -151,7 +160,8 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t addr) return cache_get_by_addr(cache, addr)->it_data; } -int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata) +int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata, + uint64_t current_age) { CacheItem *it = NULL; @@ -162,6 +172,11 @@ int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata) /* actual update of entry */ it = cache_get_by_addr(cache, addr); + if (it->it_data && it->it_addr != addr && + it->it_age + CACHED_PAGE_LIFETIME > current_age) { + /* the cache page is fresh, don't replace it */ + return -1; + } /* allocate page */ if (!it->it_data) { it->it_data = g_try_malloc(cache->page_size); @@ -174,7 +189,7 @@ int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata) memcpy(it->it_data, pdata, cache->page_size); - it->it_age = ++cache->max_item_age; + it->it_age = current_age; it->it_addr = addr; return 0; |