From: ChenLiang chenlian...@huawei.com
Avoid hot pages being replaced by others to remarkably decrease cache
misses
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}
18k pages sent compressed in 52 seconds.
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}
194k pages sent compressed in 18 seconds.
The value of cache-miss-rate decrease to 48.59%.
Signed-off-by: ChenLiang chenlian...@huawei.com
Signed-off-by: Gonglei arei.gong...@huawei.com
---
arch_init.c| 8 +---
docs/xbzrle.txt| 8
include/migration/page_cache.h | 10 +++---
page_cache.c | 23 +++
4 files changed, 39 insertions(+), 10 deletions(-)
diff --git a/arch_init.c b/arch_init.c
index 15ca4c0..84a4bd3 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_count);
}
#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_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 cc3a26a..52c8511 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 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
