I've got a world with just patches 1..5 on that's seeing corruptions, but
I've not seen where the problem is. So far the world with 1..4 on hasn't
hit those corruption, but maybe I need to test more.
Have you tested this set with google stressapptest?
Let it migrate for a few cycles with stress apptest running, then ctrl-z
the stressapptest program to let the migration complete, then fg it
to collect the results.
Dave
* arei.gong...@huawei.com (arei.gong...@huawei.com) wrote:
> 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
> 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
> 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>
> Reviewed-by: Eric Blake <ebl...@redhat.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 *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
>
>
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
