From patchwork Tue Dec 17 21:25:19 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Schoenebeck X-Patchwork-Id: 11299157 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id C1AD2138C for ; Wed, 18 Dec 2019 00:37:27 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 97CF121775 for ; Wed, 18 Dec 2019 00:37:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=crudebyte.com header.i=@crudebyte.com header.b="Tx5Sy+y0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 97CF121775 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=crudebyte.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:47732 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ihNLC-0004aV-Mw for patchwork-qemu-devel@patchwork.kernel.org; Tue, 17 Dec 2019 19:37:26 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:46637) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from <3ece7b359059bc882879d46eb8afe07466ae67ea@lizzy.crudebyte.com>) id 1ihNIN-0002nn-5K for qemu-devel@nongnu.org; Tue, 17 Dec 2019 19:34:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from <3ece7b359059bc882879d46eb8afe07466ae67ea@lizzy.crudebyte.com>) id 1ihNIM-0002tA-3F for qemu-devel@nongnu.org; Tue, 17 Dec 2019 19:34:31 -0500 Received: from lizzy.crudebyte.com ([91.194.90.13]:50165) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from <3ece7b359059bc882879d46eb8afe07466ae67ea@lizzy.crudebyte.com>) id 1ihNIL-0001df-Sw for qemu-devel@nongnu.org; Tue, 17 Dec 2019 19:34:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=lizzy; h=Message-Id:Subject:Date:Cc:To:From:Content-Type: Content-Transfer-Encoding:MIME-Version:References:In-Reply-To:Content-ID: Content-Description; bh=uy5WfovVqaMKSoia8+lCPvhLlHffgTGEIc4twNM9E+g=; b=Tx5Sy +y0LtrUST8804Xp20p2feZY/ctHH37qojLDCyn0+GigXZx347cQ4CvVOLIWIXol98VsIXTzVSuyLz FVNNXTF9RqJzIsnNH076YYE9EvosVrFp2sms1+u94hNtzGuiNjaqz6ZmYUO3uwiiGqwADQ9kNkdbN CggZs3pHjvE36Fk6zG7DZO+n01jifwE+qvrWtkVHoppaH1sEJR6NmKIaM4tzwfyhUHMwy1ZSTzBjU FjHUXi7J76TvHW5umafI8dsDaWNC9ooFdngvxxH4SF8pTLQIqK5tFM13eyE9sgC6rq6eCbSXw7vIm twephKd8hteK9v/8GXRTsYpBMmZ9w==; From: Christian Schoenebeck To: qemu-devel@nongnu.org Cc: Greg Kurz Date: Tue, 17 Dec 2019 22:25:19 +0100 Subject: [PATCH 7/9] hw/9pfs/9p-synth: avoid n-square issue in synth_readdir() Message-Id: X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 91.194.90.13 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" This patch is just a temporary benchmark hack, not intended to be merged! synth driver's readdir() implementation has a severe n-square performance problem. This patch is a quick and dirty hack to prevent that performance problem from tainting the readdir() benchmark results. Signed-off-by: Christian Schoenebeck --- hw/9pfs/9p-synth.c | 27 ++++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-) diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c index 7eb210ffa8..1743f5409f 100644 --- a/hw/9pfs/9p-synth.c +++ b/hw/9pfs/9p-synth.c @@ -225,7 +225,7 @@ static void synth_direntry(V9fsSynthNode *node, } static struct dirent *synth_get_dentry(V9fsSynthNode *dir, - struct dirent *entry, off_t off) + struct dirent *entry, off_t off, V9fsSynthNode **hack) { int i = 0; V9fsSynthNode *node; @@ -243,16 +243,37 @@ static struct dirent *synth_get_dentry(V9fsSynthNode *dir, /* end of directory */ return NULL; } + *hack = node; synth_direntry(node, entry, off); return entry; } static struct dirent *synth_readdir(FsContext *ctx, V9fsFidOpenState *fs) { - struct dirent *entry; + struct dirent *entry = NULL; V9fsSynthOpenState *synth_open = fs->private; V9fsSynthNode *node = synth_open->node; - entry = synth_get_dentry(node, &synth_open->dent, synth_open->offset); + + /* + * HACK: This is just intended for benchmark, to avoid severe n-square + * performance problem of synth driver's readdir implementation here which + * would otherwise unncessarily taint the benchmark results. By simply + * caching (globally) the previous node (of the previous synth_readdir() + * call) we can simply proceed to next node in chained list efficiently. + * + * not a good idea for any production code ;-) + */ + static struct V9fsSynthNode *cachedNode = NULL; + + if (!cachedNode) { + entry = synth_get_dentry(node, &synth_open->dent, synth_open->offset, &cachedNode); + } else { + cachedNode = cachedNode->sibling.le_next; + if (cachedNode) { + entry = &synth_open->dent; + synth_direntry(cachedNode, entry, synth_open->offset+1); + } + } if (entry) { synth_open->offset++; }