From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39596) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fnI5h-0002Lo-Np for qemu-devel@nongnu.org; Wed, 08 Aug 2018 02:37:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fnI5c-0004fC-TT for qemu-devel@nongnu.org; Wed, 08 Aug 2018 02:37:05 -0400 Received: from mail-pf1-x443.google.com ([2607:f8b0:4864:20::443]:42890) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1fnI5c-0004e9-K9 for qemu-devel@nongnu.org; Wed, 08 Aug 2018 02:37:00 -0400 Received: by mail-pf1-x443.google.com with SMTP id l9-v6so624422pff.9 for ; Tue, 07 Aug 2018 23:37:00 -0700 (PDT) References: <20180807091209.13531-1-xiaoguangrong@tencent.com> <20180807091209.13531-10-xiaoguangrong@tencent.com> <20180808060506.GH24415@xz-mi> From: Xiao Guangrong Message-ID: <2a8e132b-2944-7077-6c76-b6447d1770c5@gmail.com> Date: Wed, 8 Aug 2018 14:36:51 +0800 MIME-Version: 1.0 In-Reply-To: <20180808060506.GH24415@xz-mi> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3 09/10] migration: fix calculating xbzrle_counters.cache_miss_rate List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: pbonzini@redhat.com, mst@redhat.com, mtosatti@redhat.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, dgilbert@redhat.com, wei.w.wang@intel.com, jiang.biao2@zte.com.cn, eblake@redhat.com, Xiao Guangrong On 08/08/2018 02:05 PM, Peter Xu wrote: > On Tue, Aug 07, 2018 at 05:12:08PM +0800, guangrong.xiao@gmail.com wrote: >> From: Xiao Guangrong >> >> As Peter pointed out: >> | - xbzrle_counters.cache_miss is done in save_xbzrle_page(), so it's >> | per-guest-page granularity >> | >> | - RAMState.iterations is done for each ram_find_and_save_block(), so >> | it's per-host-page granularity >> | >> | An example is that when we migrate a 2M huge page in the guest, we >> | will only increase the RAMState.iterations by 1 (since >> | ram_find_and_save_block() will be called once), but we might increase >> | xbzrle_counters.cache_miss for 2M/4K=512 times (we'll call >> | save_xbzrle_page() that many times) if all the pages got cache miss. >> | Then IMHO the cache miss rate will be 512/1=51200% (while it should >> | actually be just 100% cache miss). >> >> And he also suggested as xbzrle_counters.cache_miss_rate is the only >> user of rs->iterations we can adapt it to count guest page numbers >> >> After that, rename 'iterations' to 'handle_pages' to better reflect >> its meaning >> >> Suggested-by: Peter Xu >> Signed-off-by: Xiao Guangrong >> --- >> migration/ram.c | 18 +++++++++--------- >> 1 file changed, 9 insertions(+), 9 deletions(-) >> >> diff --git a/migration/ram.c b/migration/ram.c >> index 09be01dca2..bd7c18d1f9 100644 >> --- a/migration/ram.c >> +++ b/migration/ram.c >> @@ -300,10 +300,10 @@ struct RAMState { >> uint64_t num_dirty_pages_period; >> /* xbzrle misses since the beginning of the period */ >> uint64_t xbzrle_cache_miss_prev; >> - /* number of iterations at the beginning of period */ >> - uint64_t iterations_prev; >> - /* Iterations since start */ >> - uint64_t iterations; >> + /* total handled pages at the beginning of period */ >> + uint64_t handle_pages_prev; >> + /* total handled pages since start */ >> + uint64_t handle_pages; > > The name is not that straightforward to me. I would think about > "[guest|host]_page_count" or something better, or we just keep the old > naming but with a better comment would be fine too. The filed actually indicates total pages (target pages more precisely) handled during live migration. 'iterations' confuses us completely. It's target_page_count good to you? > >> /* number of dirty bits in the bitmap */ >> uint64_t migration_dirty_pages; >> /* last dirty_sync_count we have seen */ >> @@ -1587,19 +1587,19 @@ uint64_t ram_pagesize_summary(void) >> >> static void migration_update_rates(RAMState *rs, int64_t end_time) >> { >> - uint64_t iter_count = rs->iterations - rs->iterations_prev; >> + uint64_t page_count = rs->handle_pages - rs->handle_pages_prev; >> >> /* calculate period counters */ >> ram_counters.dirty_pages_rate = rs->num_dirty_pages_period * 1000 >> / (end_time - rs->time_last_bitmap_sync); >> >> - if (!iter_count) { >> + if (!page_count) { >> return; >> } >> >> if (migrate_use_xbzrle()) { >> xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss - >> - rs->xbzrle_cache_miss_prev) / iter_count; >> + rs->xbzrle_cache_miss_prev) / page_count; >> rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss; >> } >> } >> @@ -1657,7 +1657,7 @@ static void migration_bitmap_sync(RAMState *rs) >> >> migration_update_rates(rs, end_time); >> >> - rs->iterations_prev = rs->iterations; >> + rs->handle_pages_prev = rs->handle_pages; >> >> /* reset period counters */ >> rs->time_last_bitmap_sync = end_time; >> @@ -3209,7 +3209,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque) >> break; >> } >> >> - rs->iterations++; >> + rs->handle_pages += pages; > > So it's still counting host pages, is this your intention to only > change the name in the patch? Hmm... the value returned by ram_find_and_save_block() isn't the total target pages posted out? /** * ram_find_and_save_block: finds a dirty page and sends it to f * * Called within an RCU critical section. * * Returns the number of pages written where zero means no dirty pages, * or negative on error ... * * On systems where host-page-size > target-page-size it will send all the * pages in a host page that are dirty. */