From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44997) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YJlya-0005Iz-Qh for qemu-devel@nongnu.org; Fri, 06 Feb 2015 11:41:53 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YJlyU-0000vi-Oo for qemu-devel@nongnu.org; Fri, 06 Feb 2015 11:41:52 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56249) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YJlyU-0000vU-Hr for qemu-devel@nongnu.org; Fri, 06 Feb 2015 11:41:46 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t16GfjiU026887 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Fri, 6 Feb 2015 11:41:46 -0500 From: Kevin Wolf Date: Fri, 6 Feb 2015 17:40:48 +0100 Message-Id: <1423240849-15499-42-git-send-email-kwolf@redhat.com> In-Reply-To: <1423240849-15499-1-git-send-email-kwolf@redhat.com> References: <1423240849-15499-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PULL 41/42] block: Give always priority to unused entries in the qcow2 L2 cache List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kwolf@redhat.com From: Alberto Garcia The current algorithm to replace entries from the L2 cache gives priority to newer hits by dividing the hit count of all existing entries by two everytime there is a cache miss. However, if there are several cache misses the hit count of the existing entries can easily go down to 0. This will result in those entries being replaced even when there are others that have never been used. This problem is more noticeable with larger disk images and cache sizes, since the chances of having several misses before the cache is full are higher. If we make sure that the hit count can never go down to 0 again, unused entries will always have priority. Signed-off-by: Alberto Garcia Reviewed-by: Max Reitz Signed-off-by: Kevin Wolf --- block/qcow2-cache.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c index 904f6b1..b115549 100644 --- a/block/qcow2-cache.c +++ b/block/qcow2-cache.c @@ -253,7 +253,9 @@ static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c) /* Give newer hits priority */ /* TODO Check how to optimize the replacement strategy */ - c->entries[i].cache_hits /= 2; + if (c->entries[i].cache_hits > 1) { + c->entries[i].cache_hits /= 2; + } } if (min_index == -1) { -- 1.8.3.1