From: ChenLiang <chenlian...@huawei.com>
Avoid hot pages being replaced by others to remarkably decrease cache
Sample results with the test program which quote from xbzrle.txt ran in
vm:(migrate bandwidth:1GE and xbzrle cache size 8MB)
the test program:
include <stdlib.h>
include <stdio.h>
int main()
{
char *buf = (char *) calloc(4096, 4096);
while (1) {
int i;
for (i = 0; i < 4096 * 4; i++) {
buf[i * 4096 / 4]++;
}
printf(".");
}
}
before this patch:
virsh qemu-monitor-command test_vm '{"execute": "query-migrate"}'
{"return":{"expected-downtime":1020,"xbzrle-cache":{"bytes":1108284,
"cache-size":8388608,"cache-miss-rate":0.987013,"pages":18297,"overflow":8,
"cache-miss":1228737},"status":"active","setup-time":10,"total-time":52398,
"ram":{"total":12466991104,"remaining":1695744,"mbps":935.559472,
"transferred":5780760580,"dirty-sync-counter":271,"duplicate":2878530,
"dirty-pages-rate":29130,"skipped":0,"normal-bytes":5748592640,
"normal":1403465}},"id":"libvirt-706"}
cache-miss-rate is 98.7%, totally miss.
after optimizing:
virsh qemu-monitor-command test_vm '{"execute": "query-migrate"}'
{"return":{"expected-downtime":2054,"xbzrle-cache":{"bytes":5066763,
"cache-size":8388608,"cache-miss-rate":0.485924,"pages":194823,"overflow":0,
"cache-miss":210653},"status":"active","setup-time":11,"total-time":18729,
"ram":{"total":12466991104,"remaining":3895296,"mbps":937.663549,
"transferred":1615042219,"dirty-sync-counter":98,"duplicate":2869840,
"dirty-pages-rate":58781,"skipped":0,"normal-bytes":1588404224,
"normal":387794}},"id":"libvirt-266"}
The value of cache-miss-rate decrease 49.13%.
Signed-off-by: ChenLiang <chenlian...@huawei.com>
Signed-off-by: Gonglei <arei.gong...@huawei.com>
---
arch_init.c | 8 +++++---
include/migration/page_cache.h | 10 +++++++---
page_cache.c | 23 +++++++++++++++++++----
3 files changed, 31 insertions(+), 10 deletions(-)
diff --git a/arch_init.c b/arch_init.c
index 9ceb22e..21d9cf6 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -343,7 +343,8 @@ 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_counter);
}
#define ENCODING_FLAG_XBZRLE 0x1
@@ -355,10 +356,11 @@ 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_counter)) {
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_counter) == -1) {
return -1;
} else {
/* update *current_data when the page has been
diff --git a/include/migration/page_cache.h b/include/migration/page_cache.h
index 2d5ce2d..10ed532 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 b033681..c78157b 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 {
@@ -121,7 +124,8 @@ 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;
@@ -130,7 +134,12 @@ 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)
@@ -150,7 +159,8 @@ 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;
@@ -161,6 +171,11 @@ 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_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);
@@ -173,7 +188,7 @@ 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;
--
1.7.12.4
