qemu/include/migration/page_cache.h
ChenLiang 27af7d6ea5 xbzrle: optimize XBZRLE to decrease the cache misses
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 <chenliang88@huawei.com>
Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
2015-01-15 17:49:43 +05:30

87 lines
2.2 KiB
C

/*
* Page cache for QEMU
* The cache is base on a hash of the page address
*
* Copyright 2012 Red Hat, Inc. and/or its affiliates
*
* Authors:
* Orit Wasserman <owasserm@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#ifndef PAGE_CACHE_H
#define PAGE_CACHE_H
/* Page cache for storing guest pages */
typedef struct PageCache PageCache;
/**
* cache_init: Initialize the page cache
*
*
* Returns new allocated cache or NULL on error
*
* @cache pointer to the PageCache struct
* @num_pages: cache maximal number of cached pages
* @page_size: cache page size
*/
PageCache *cache_init(int64_t num_pages, unsigned int page_size);
/**
* cache_fini: free all cache resources
* @cache pointer to the PageCache struct
*/
void cache_fini(PageCache *cache);
/**
* cache_is_cached: Checks to see if the page is cached
*
* Returns %true if page is cached
*
* @cache pointer to the PageCache struct
* @addr: page addr
* @current_age: current bitmap generation
*/
bool cache_is_cached(const PageCache *cache, uint64_t addr,
uint64_t current_age);
/**
* get_cached_data: Get the data cached for an addr
*
* Returns pointer to the data cached or NULL if not cached
*
* @cache pointer to the PageCache struct
* @addr: page addr
*/
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 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,
uint64_t current_age);
/**
* cache_resize: resize the page cache. In case of size reduction the extra
* pages will be freed
*
* Returns -1 on error new cache size on success
*
* @cache pointer to the PageCache struct
* @num_pages: new page cache size (in pages)
*/
int64_t cache_resize(PageCache *cache, int64_t num_pages);
#endif