From patchwork Fri May 22 15:26:26 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 475669 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 861911402A5 for ; Sat, 23 May 2015 01:33:50 +1000 (AEST) Received: from localhost ([::1]:34616 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YvoxI-00080H-Gz for incoming@patchwork.ozlabs.org; Fri, 22 May 2015 11:33:48 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42713) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yvoqk-0004Zw-1j for qemu-devel@nongnu.org; Fri, 22 May 2015 11:27:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Yvoqi-0006fQ-Nq for qemu-devel@nongnu.org; Fri, 22 May 2015 11:27:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52003) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yvoqc-0006Ye-I7; Fri, 22 May 2015 11:26:54 -0400 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (Postfix) with ESMTPS id 3FCF38EA5B; Fri, 22 May 2015 15:26:54 +0000 (UTC) Received: from noname.redhat.com (ovpn-116-82.ams2.redhat.com [10.36.116.82]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t4MFQf9Z016774; Fri, 22 May 2015 11:26:53 -0400 From: Kevin Wolf To: qemu-block@nongnu.org Date: Fri, 22 May 2015 17:26:26 +0200 Message-Id: <1432308400-13958-9-git-send-email-kwolf@redhat.com> In-Reply-To: <1432308400-13958-1-git-send-email-kwolf@redhat.com> References: <1432308400-13958-1-git-send-email-kwolf@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.24 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: kwolf@redhat.com, qemu-devel@nongnu.org Subject: [Qemu-devel] [PULL 08/22] qcow2: remove qcow2_cache_find_entry_to_replace() X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org From: Alberto Garcia A cache miss means that the whole array was traversed and the entry we were looking for was not found, so there's no need to traverse it again in order to select an entry to replace. Signed-off-by: Alberto Garcia Reviewed-by: Stefan Hajnoczi Reviewed-by: Max Reitz Signed-off-by: Kevin Wolf --- block/qcow2-cache.c | 45 ++++++++++++++++----------------------------- 1 file changed, 16 insertions(+), 29 deletions(-) diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c index 3a31895..2035cd8 100644 --- a/block/qcow2-cache.c +++ b/block/qcow2-cache.c @@ -242,51 +242,38 @@ int qcow2_cache_empty(BlockDriverState *bs, Qcow2Cache *c) return 0; } -static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c) -{ - int i; - uint64_t min_lru_counter = UINT64_MAX; - int min_index = -1; - - - for (i = 0; i < c->size; i++) { - if (c->entries[i].ref) { - continue; - } - - if (c->entries[i].lru_counter < min_lru_counter) { - min_index = i; - min_lru_counter = c->entries[i].lru_counter; - } - } - - if (min_index == -1) { - /* This can't happen in current synchronous code, but leave the check - * here as a reminder for whoever starts using AIO with the cache */ - abort(); - } - return min_index; -} - static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset, void **table, bool read_from_disk) { BDRVQcowState *s = bs->opaque; int i; int ret; + uint64_t min_lru_counter = UINT64_MAX; + int min_lru_index = -1; trace_qcow2_cache_get(qemu_coroutine_self(), c == s->l2_table_cache, offset, read_from_disk); /* Check if the table is already cached */ for (i = 0; i < c->size; i++) { - if (c->entries[i].offset == offset) { + const Qcow2CachedTable *t = &c->entries[i]; + if (t->offset == offset) { goto found; } + if (t->ref == 0 && t->lru_counter < min_lru_counter) { + min_lru_counter = t->lru_counter; + min_lru_index = i; + } + } + + if (min_lru_index == -1) { + /* This can't happen in current synchronous code, but leave the check + * here as a reminder for whoever starts using AIO with the cache */ + abort(); } - /* If not, write a table back and replace it */ - i = qcow2_cache_find_entry_to_replace(c); + /* Cache miss: write a table back and replace it */ + i = min_lru_index; trace_qcow2_cache_get_replace_entry(qemu_coroutine_self(), c == s->l2_table_cache, i); if (i < 0) {