From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55830) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WJK7Z-0007Wm-JS for qemu-devel@nongnu.org; Fri, 28 Feb 2014 04:52:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WJK7U-0002va-Q3 for qemu-devel@nongnu.org; Fri, 28 Feb 2014 04:52:45 -0500 Received: from mx1.redhat.com ([209.132.183.28]:60781) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WJK7U-0002vQ-Hm for qemu-devel@nongnu.org; Fri, 28 Feb 2014 04:52:40 -0500 Date: Fri, 28 Feb 2014 09:51:26 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20140228095125.GD2695@work-vm> References: <33183CC9F5247A488A2544077AF19020815D2280@SZXEMA503-MBS.china.huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33183CC9F5247A488A2544077AF19020815D2280@SZXEMA503-MBS.china.huawei.com> Subject: Re: [Qemu-devel] [PATCH 3/7] XBZRLE: optimize XBZRLE to decrease the cache missing List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Gonglei (Arei)" Cc: "chenliang (T)" , Peter Maydell , Juan Quintela , "pl@kamp.de" , "qemu-devel@nongnu.org" , "aliguori@amazon.com" , "pbonzini@redhat.com" * Gonglei (Arei) (arei.gonglei@huawei.com) wrote: > Avoid the hot pages cache replacing by others to remarkable decrease cache > missing. The counter of updating dirty bitmap is used to indicate the cached > page age. It seems worth noting that you've changed 'it_age's use - that's ok, but perhaps not obvious. Also, the change in the behaviour of cache_insert to 'fail' when it decides not to insert a page is not obvious. > Signed-off-by: ChenLiang > Signed-off-by: Gonglei > --- > arch_init.c | 8 +++++--- > include/migration/page_cache.h | 8 ++++++-- > page_cache.c | 19 +++++++++++++++---- > 3 files changed, 26 insertions(+), 9 deletions(-) > > diff --git a/arch_init.c b/arch_init.c > index 6823c5a..fc71331 100644 > --- a/arch_init.c > +++ b/arch_init.c > @@ -315,7 +315,8 @@ 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, > + get_bitmap_sync_cnt()); > } > > #define ENCODING_FLAG_XBZRLE 0x1 > @@ -327,10 +328,11 @@ 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, get_bitmap_sync_cnt())) { > 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, > + get_bitmap_sync_cnt()) == -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..cadce55 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 indicate age of the page if cache hit > */ > -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 > @@ -65,8 +67,10 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t addr); > * @cache pointer to the PageCache struct > * @addr: page address > * @pdata: pointer to the page > + * @current_age indicate age of the page if the page is inserted into cache > */ > -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); The comment on cache_insert needs changing, it currently says: * Returns -1 on error that's not true any more, it'll return -1 on error or if it just decided that it's better not to cache it. > /** > * 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..fa58ab2 100644 > --- a/page_cache.c > +++ b/page_cache.c > @@ -121,7 +121,8 @@ 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 +131,12 @@ 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) { > + /* updata the it_age when the cache hit */ Typo: updata -> update > + 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 +156,8 @@ 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 +168,10 @@ 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 != NULL) && (it->it_age + 2 > current_age)) { > + /* the cache page is fresh, don't replace it */ > + return -1; > + } A magical constant '2' - should probably a define/const somewhere. > /* allocate page */ > if (!it->it_data) { > it->it_data = g_try_malloc(cache->page_size); > @@ -173,7 +184,7 @@ 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; Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK