From patchwork Thu Sep 3 14:20:21 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Schoenebeck X-Patchwork-Id: 305261 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.4 required=3.0 tests=BAYES_00, DATE_IN_PAST_96_XX, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1551AC433E2 for ; Wed, 16 Sep 2020 09:57:30 +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 A42E421973 for ; Wed, 16 Sep 2020 09:57:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=crudebyte.com header.i=@crudebyte.com header.b="NmLpvV0Y" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A42E421973 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+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:36968 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kIUBs-0005aj-Po for qemu-devel@archiver.kernel.org; Wed, 16 Sep 2020 05:57:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53982) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <62777d825ba6a7f9ba749588a9e1e7b273f7e967@lizzy.crudebyte.com>) id 1kIU8A-00081W-4o for qemu-devel@nongnu.org; Wed, 16 Sep 2020 05:53:38 -0400 Received: from lizzy.crudebyte.com ([91.194.90.13]:45719) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from <62777d825ba6a7f9ba749588a9e1e7b273f7e967@lizzy.crudebyte.com>) id 1kIU88-0000fG-HS for qemu-devel@nongnu.org; Wed, 16 Sep 2020 05:53:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=lizzy; h=Cc:To:Subject:Date:From:References:In-Reply-To: Message-Id:Content-Type:Content-Transfer-Encoding:MIME-Version:Content-ID: Content-Description; bh=IOxEdH7P12wqsQCMQXkcjSgsqCj59UF4YaQI8tHT/fE=; b=NmLpv V0YG5bbsMlo42pNRSY4xDSK0yF9nWneWlv8XaqZh65pgUE4191Tr+aoXtYhirIVTeZ7hmFilJoIaW PP21I5r/5gHvKubQYFR3C240PDorO38sO0dWATiZ2pv0ZQSOrG4ohbls67m7ULwV3s813Zu1cAVv3 1ORGfwEFxLo5WPJJBJ4s7rzUYQoLVDizL0BQj6kuNjvn38/Gpf2QgWWB6EnV7fv0RpB1pEwdD/SKK zB4M2v8ICPlX97AtHzvQYzwPVUy76VoBgdc72TSs894Pg0Fx6Fw6O+YdKOiBjizfxxNv0PAJCaeHN ck0lkJc9+va+sJM19h3HV35QRS9SA==; Message-Id: <62777d825ba6a7f9ba749588a9e1e7b273f7e967.1600166281.git.qemu_oss@crudebyte.com> In-Reply-To: References: From: Christian Schoenebeck Date: Thu, 3 Sep 2020 16:20:21 +0200 Subject: [PULL 1/2] 9pfs: log warning if msize <= 8192 To: qemu-devel@nongnu.org, Peter Maydell Cc: Greg Kurz Received-SPF: none client-ip=91.194.90.13; envelope-from=62777d825ba6a7f9ba749588a9e1e7b273f7e967@lizzy.crudebyte.com; helo=lizzy.crudebyte.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/16 05:20:12 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: 13 X-Spam_score: 1.3 X-Spam_bar: + X-Spam_report: (1.3 / 5.0 requ) BAYES_00=-1.9, DATE_IN_PAST_96_XX=3.405, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=no autolearn_force=no X-Spam_action: no action 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" It is essential to choose a reasonable high value for 'msize' to avoid severely degraded file I/O performance. This parameter can only be chosen on client/guest side, and a Linux client defaults to an 'msize' of only 8192 if the user did not explicitly specify a value for 'msize', which results in very poor file I/O performance. Unfortunately many users are not aware that they should specify an appropriate value for 'msize' to avoid severe performance issues, so log a performance warning (with a QEMU wiki link explaining this issue in detail) on host side in that case to make it more clear. Currently a client cannot automatically pick a reasonable value for 'msize', because a good value for 'msize' depends on the file I/O potential of the underlying storage on host side, i.e. a feature invisible to the client, and even then a user would still need to trade off between performance profit and additional RAM costs, i.e. with growing 'msize' (RAM occupation), performance still increases, but performance delta will shrink continuously. Signed-off-by: Christian Schoenebeck Reviewed-by: Greg Kurz Message-Id: Signed-off-by: Christian Schoenebeck --- hw/9pfs/9p.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c index 7bb994bbf2..99b6f24fd6 100644 --- a/hw/9pfs/9p.c +++ b/hw/9pfs/9p.c @@ -1353,6 +1353,15 @@ static void coroutine_fn v9fs_version(void *opaque) goto out; } + /* 8192 is the default msize of Linux clients */ + if (s->msize <= 8192) { + warn_report_once( + "9p: degraded performance: a reasonable high msize should be " + "chosen on client/guest side (chosen msize is <= 8192). See " + "https://wiki.qemu.org/Documentation/9psetup#msize for details." + ); + } + marshal: err = pdu_marshal(pdu, offset, "ds", s->msize, &version); if (err < 0) {