From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33106) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fnHay-0000iM-O5 for qemu-devel@nongnu.org; Wed, 08 Aug 2018 02:05:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fnHav-0001ra-Rj for qemu-devel@nongnu.org; Wed, 08 Aug 2018 02:05:20 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:41134 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fnHav-0001qE-G6 for qemu-devel@nongnu.org; Wed, 08 Aug 2018 02:05:17 -0400 Date: Wed, 8 Aug 2018 14:05:06 +0800 From: Peter Xu Message-ID: <20180808060506.GH24415@xz-mi> References: <20180807091209.13531-1-xiaoguangrong@tencent.com> <20180807091209.13531-10-xiaoguangrong@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180807091209.13531-10-xiaoguangrong@tencent.com> 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: guangrong.xiao@gmail.com 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 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. > /* 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? > > /* we want to check in the 1st loop, just in case it was the 1st time > and we had to sync the dirty bitmap. > -- > 2.14.4 > Regards, -- Peter Xu