From mboxrd@z Thu Jan 1 00:00:00 1970 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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 5DFEDC433E0 for ; Mon, 22 Feb 2021 15:10:26 +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 EA41B6186A for ; Mon, 22 Feb 2021 15:10:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EA41B6186A 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]:48150 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lECqu-0007SQ-Pf for qemu-devel@archiver.kernel.org; Mon, 22 Feb 2021 10:10:24 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:56264) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lECpS-00061v-KC for qemu-devel@nongnu.org; Mon, 22 Feb 2021 10:08:54 -0500 Received: from kylie.crudebyte.com ([5.189.157.229]:52457) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lECpP-0007Vy-M7 for qemu-devel@nongnu.org; Mon, 22 Feb 2021 10:08:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=kylie; h=Content-Type:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Content-ID:Content-Description; bh=JLLeQmi9DpenY3Dn8HPkpgtAJyFWma2HGbFQFaACmWc=; b=L9tevkE2x1Z4+Ju9ZWXk75MDwU 90y4vC865ThlO0YiGZSPBNPGMbtEp4aETq9D6FSFkNDyEGS1JYAfl7LQ2wYbM1b0NG2mCUKyBfUWZ X5WfLekc7/GxwYi5UZNELRiXM0UYzt3dM/0hxQb12AJpuBRfDyOBSQRNj3eKBQajasdfR+pLXvNWy 5Xnb+TfLI2Wb2YS104+HogaQRwuLcmNw4W9yEh+FHthB+fPRu7yU2D2CnXDM9xj+spDPtoBzNiEuB 0nruYgE752vA6dhxsLwKw4uXApBYVxNK+938v9BfKgsL7k6kkr9umjpGGZQ7V1wUgndQOdkPGHR8S h4IuDn5Ah8FXb1rtfGWpPYQi6we2Nj5CPHJPOIga5mhIFQDIEvo2d3cOuXbES/2N7XIznO3tsXuTl kU+Q+rgk7Xm34v4v1U6L/dlv5qCci0nT0UzhAO/BQ1sV9KhSv++3+qUQBsGF5rMJ8XMvTmBxwF64L uO3+As8PKGwuDD5TbJmW4iFUifIO3Cqlcz7ic2PXaE0PCnc+KYkLy/rdNMdRLKa/7nIYMK0xiaeA2 WTLIl8ujVoS3UKn9uZKmqxV5dde7cwyOPaFU+bc6/scTvV2GfyE8ophLMcXkpN2xPgo9LjgEYXqXS t2NiAUYJJukhF2WhROJ6/d6SgwtvTEW/kXePXIUQU=; From: Christian Schoenebeck To: qemu-devel@nongnu.org Cc: Greg Kurz , "Venegas Munoz, Jose Carlos" , "cdupontd@redhat.com" , virtio-fs-list , "Dr. David Alan Gilbert" , Stefan Hajnoczi , "Shinde, Archana M" , Vivek Goyal Subject: Re: Can not set high msize with virtio-9p (Was: Re: virtiofs vs 9p performance) Date: Mon, 22 Feb 2021 16:08:04 +0100 Message-ID: <2848338.ij5OB8EVuP@silver> In-Reply-To: <20210222131814.28e06428@bahia.lan> References: <20200918213436.GA3520@redhat.com> <2337260.PURPEL5hZR@silver> <20210222131814.28e06428@bahia.lan> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Received-SPF: pass client-ip=5.189.157.229; envelope-from=qemu_oss@crudebyte.com; helo=kylie.crudebyte.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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" On Montag, 22. Februar 2021 13:18:14 CET Greg Kurz wrote: > On Sat, 20 Feb 2021 16:38:35 +0100 > > Christian Schoenebeck wrote: > > On Freitag, 19. Februar 2021 20:01:12 CET Vivek Goyal wrote: > > > On Fri, Feb 19, 2021 at 06:33:46PM +0100, Christian Schoenebeck wrote: > > > > On Freitag, 19. Februar 2021 17:08:48 CET Vivek Goyal wrote: > > > > > On Fri, Sep 25, 2020 at 10:06:41AM +0200, Christian Schoenebeck wrote: > > > > > > On Freitag, 25. September 2020 00:10:23 CEST Vivek Goyal wrote: > > > > > > > In my testing, with cache=none, virtiofs performed better than > > > > > > > 9p in > > > > > > > all the fio jobs I was running. For the case of cache=auto for > > > > > > > virtiofs > > > > > > > (with xattr enabled), 9p performed better in certain write > > > > > > > workloads. I > > > > > > > have identified root cause of that problem and working on > > > > > > > HANDLE_KILLPRIV_V2 patches to improve WRITE performance of > > > > > > > virtiofs > > > > > > > with cache=auto and xattr enabled. > > > > > > > > > > > > Please note, when it comes to performance aspects, you should set > > > > > > a > > > > > > reasonable high value for 'msize' on 9p client side: > > > > > > https://wiki.qemu.org/Documentation/9psetup#msize > > > > > > > > > > Hi Christian, > > > > > > > > > > I am not able to set msize to a higher value. If I try to specify > > > > > msize > > > > > 16MB, and then read back msize from /proc/mounts, it sees to cap it > > > > > at 512000. Is that intended? > > > > > > > > 9p server side in QEMU does not perform any msize capping. The code in > > > > this > > > > case is very simple, it's just what you see in function > > > > v9fs_version(): > > > > > > > > https://github.com/qemu/qemu/blob/6de76c5f324904c93e69f9a1e8e4fd0bd6f6 > > > > b57a > > > > /hw/9pfs/9p.c#L1332> > > > > > > > > > $ mount -t 9p -o > > > > > trans=virtio,version=9p2000.L,cache=none,msize=16777216 > > > > > hostShared /mnt/virtio-9p > > > > > > > > > > $ cat /proc/mounts | grep 9p > > > > > hostShared /mnt/virtio-9p 9p > > > > > rw,sync,dirsync,relatime,access=client,msize=512000,trans=virtio 0 0 > > > > > > > > > > I am using 5.11 kernel. > > > > > > > > Must be something on client (guest kernel) side. I don't see this here > > > > with > > > > guest kernel 4.9.0 happening with my setup in a quick test: > > > > > > > > $ cat /etc/mtab | grep 9p > > > > svnRoot / 9p > > > > rw,dirsync,relatime,trans=virtio,version=9p2000.L,msize=104857600,cach > > > > e=m > > > > map 0 0 $ > > > > > > > > Looks like the root cause of your issue is this: > > > > > > > > struct p9_client *p9_client_create(const char *dev_name, char > > > > *options) > > > > { > > > > > > > > ... > > > > if (clnt->msize > clnt->trans_mod->maxsize) > > > > > > > > clnt->msize = clnt->trans_mod->maxsize; > > > > > > > > https://github.com/torvalds/linux/blob/f40ddce88593482919761f74910f42f > > > > 4b84 > > > > c004b/net/9p/client.c#L1045 > > > > > > That was introduced by a patch 2011. > > > > > > commit c9ffb05ca5b5098d6ea468c909dd384d90da7d54 > > > Author: Venkateswararao Jujjuri (JV) > > > Date: Wed Jun 29 18:06:33 2011 -0700 > > > > > > net/9p: Fix the msize calculation. > > > > > > msize represents the maximum PDU size that includes P9_IOHDRSZ. > > > > > > You kernel 4.9 is newer than this. So most likely you have this commit > > > too. I will spend some time later trying to debug this. > > > > > > Vivek > > Hi Vivek and Christian, > > I reproduce with an up-to-date fedora rawhide guest. > > Capping comes from here: > > net/9p/trans_virtio.c: .maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3), > > i.e. 4096 * (128 - 3) == 512000 > > AFAICT this has been around since 2011, i.e. always for me as a > maintainer and I admit I had never tried such high msize settings > before. > > commit b49d8b5d7007a673796f3f99688b46931293873e > Author: Aneesh Kumar K.V > Date: Wed Aug 17 16:56:04 2011 +0000 > > net/9p: Fix kernel crash with msize 512K > > With msize equal to 512K (PAGE_SIZE * VIRTQUEUE_NUM), we hit multiple > crashes. This patch fix those. > > Signed-off-by: Aneesh Kumar K.V > Signed-off-by: Eric Van Hensbergen > > Changelog doesn't help much but it looks like it was a bandaid > for some more severe issues. I did not ever have a kernel crash when I boot a Linux guest with a 9pfs root fs and 100 MiB msize. Should we ask virtio or 9p Linux client maintainers if they can add some info what this is about? > > As the kernel code sais trans_mod->maxsize, maybe its something in virtio > > on qemu side that does an automatic step back for some reason. I don't > > see something in the 9pfs virtio transport driver > > (hw/9pfs/virtio-9p-device.c on QEMU side) that would do this, so I would > > also need to dig deeper. > > > > Do you have some RAM limitation in your setup somewhere? > > > > For comparison, this is how I started the VM: > > > > ~/git/qemu/build/qemu-system-x86_64 \ > > -machine pc,accel=kvm,usb=off,dump-guest-core=off -m 2048 \ > > -smp 4,sockets=4,cores=1,threads=1 -rtc base=utc \ > > -boot strict=on -kernel /home/bee/vm/stretch/boot/vmlinuz-4.9.0-13-amd64 \ > > -initrd /home/bee/vm/stretch/boot/initrd.img-4.9.0-13-amd64 \ > > -append 'root=svnRoot rw rootfstype=9p > > rootflags=trans=virtio,version=9p2000.L,msize=104857600,cache=mmap > > console=ttyS0' \ > First obvious difference I see between your setup and mine is that > you're mounting the 9pfs as root from the kernel command line. For > some reason, maybe this has an impact on the check in p9_client_create() ? > > Can you reproduce with a scenario like Vivek's one ? Yep, confirmed. If I boot a guest from an image file first and then try to manually mount a 9pfs share after guest booted, then I get indeed that msize capping of just 512 kiB as well. That's far too small. :/ Best regards, Christian Schoenebeck