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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B2C28C433EF for ; Thu, 30 Dec 2021 14:12:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239819AbhL3OMP (ORCPT ); Thu, 30 Dec 2021 09:12:15 -0500 Received: from lizzy.crudebyte.com ([91.194.90.13]:37057 "EHLO lizzy.crudebyte.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233197AbhL3OMO (ORCPT ); Thu, 30 Dec 2021 09:12:14 -0500 X-Greylist: delayed 2521 seconds by postgrey-1.27 at vger.kernel.org; Thu, 30 Dec 2021 09:12:13 EST DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=crudebyte.com; s=lizzy; h=Cc:To:Subject:Date:From:Message-Id:Content-Type: Content-Transfer-Encoding:MIME-Version:References:In-Reply-To:Content-ID: Content-Description; bh=v0FOFCtrEu0tqoBce1riXue0DcgvfXWSveZUomzIpD4=; b=BZj7L 5m6l9r8vB6k8aP9uI7khIbEuDNZucTxSLVLnaS41A8DoV9OlbsUeDDeIH9F+4AH4a5hRmP7ssAoTv PmP7KrFnJHRg5piFl0M1Y37OPiKfzsQLFBZGyJ5mFsPBQ2/JJXm+A4sLglk6wAaJX1ujBXBBrbwwZ 72C39ZjXiV+vCGqkKMTWapynerxbSoc3nHPvStUagQW5HfyvkC98V91n00LicDK0Ey/cg1VwF2oU7 TzIj9JcJ9nXFPqsNYy3JUCPoeK4KZlgo+w2D+fnI5u75+MVFdoO9tEo0OBEA2xfHzrPLZG+ehgEPW HTi5lg20afzXR825VuA7lHQEOxvmA==; Message-Id: From: Christian Schoenebeck Date: Thu, 30 Dec 2021 14:23:18 +0100 Subject: [PATCH v4 00/12] remove msize limit in virtio transport To: v9fs-developer@lists.sourceforge.net Cc: netdev@vger.kernel.org, Dominique Martinet , Eric Van Hensbergen , Latchesar Ionkov , Greg Kurz , Vivek Goyal , Nikolay Kichukov Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org This series aims to get get rid of the current 500k 'msize' limitation in the 9p virtio transport, which is currently a bottleneck for performance of 9p mounts. To avoid confusion: it does remove the msize limit for the virtio transport, on 9p client level though the anticipated milestone for this series is now a max. 'msize' of 4 MB. See patch 8 for reason why. This is a follow-up of the following series and discussion: https://lore.kernel.org/netdev/cover.1632327421.git.linux_oss@crudebyte.com/ Latest version of this series: https://github.com/cschoenebeck/linux/commits/9p-virtio-drop-msize-cap OVERVIEW OF PATCHES: * Patch 1 is just a trivial info message for the user to know why his msize option got ignored by 9p client in case the value was larger than what is supported by this 9p driver. * Patches 2..7 remove the msize limitation from the 'virtio' transport (i.e. the 9p 'virtio' transport itself actually supports >4MB now, tested successfully with an experimental QEMU version and some dirty 9p Linux client hacks up to msize=128MB). * Patch 8 limits msize for all transports to 4 MB for now as >4MB would need more work on 9p client level (see commit log of patch 8 for details). * Patches 9..12 tremendously reduce unnecessarily huge 9p message sizes and therefore provide performance gain as well. So far, almost all 9p messages simply allocated message buffers exactly msize large, even for messages that actually just needed few bytes. So these patches make sense by themselves, independent of this overall series, however for this series even more, because the larger msize, the more this issue would have hurt otherwise. PREREQUISITES: If you are testing with QEMU then please either use latest QEMU 6.2 release or higher, or at least apply the following patch on QEMU side: https://lore.kernel.org/qemu-devel/E1mT2Js-0000DW-OH@lizzy.crudebyte.com/ That QEMU patch is required if you are using a user space app that automatically retrieves an optimum I/O block size by obeying stat's st_blksize, which 'cat' for instance is doing, e.g.: time cat test_rnd.dat > /dev/null Otherwise please use a user space app for performance testing that allows you to force a large block size and to avoid that QEMU issue, like 'dd' for instance, in that case you don't need to patch QEMU. KNOWN LIMITATION: With this series applied I can run QEMU host <-> 9P virtio <-> Linux guest with up to slightly below 4 MB msize [4186112 = (1024-2) * 4096]. If I try to run it with exactly 4 MB (4194304) it currently hits a limitation on QEMU side: qemu-system-x86_64: virtio: too many write descriptors in indirect table That's because QEMU currently has a hard coded limit of max. 1024 virtio descriptors per vring slot (i.e. per virtio message), see to do (1.) below. STILL TO DO: 1. Negotiating virtio "Queue Indirect Size" (MANDATORY): The QEMU issue described above must be addressed by negotiating the maximum length of virtio indirect descriptor tables on virtio device initialization. This would not only avoid the QEMU error above, but would also allow msize of >4MB in future. Before that change can be done on Linux and QEMU sides though, it first requires a change to the virtio specs. Work on that on the virtio specs is in progress: https://github.com/oasis-tcs/virtio-spec/issues/122 This is not really an issue for testing this series. Just stick to max. msize=4186112 as described above and you will be fine. However for the final PR this should obviously be addressed in a clean way. 2. Reduce readdir buffer sizes (optional - maybe later): This series already reduced the message buffers for most 9p message types. This does not include Treaddir though yet, which is still simply using msize. It would make sense to benchmark first whether this is actually an issue that hurts. If it does, then one might use already existing vfs knowledge to estimate the Treaddir size, or starting with some reasonable hard coded small Treaddir size first and then increasing it just on the 2nd Treaddir request if there are more directory entries to fetch. 3. Add more buffer caches (optional - maybe later): p9_fcall_init() uses kmem_cache_alloc() instead of kmalloc() for very large buffers to reduce latency waiting for memory allocation to complete. Currently it does that only if the requested buffer size is exactly msize large. As patch 11 already divided the 9p message types into few message size categories, maybe it would make sense to use e.g. 4 separate caches for those memory category (e.g. 4k, 8k, msize/2, msize). Might be worth a benchmark test. Testing and feedback appreciated! v3 -> v4: * Limit msize to 4 MB for all transports [NEW patch 8]. * Avoid unnecessarily huge 9p message buffers [NEW patch 9] .. [NEW patch 12]. Christian Schoenebeck (12): net/9p: show error message if user 'msize' cannot be satisfied 9p/trans_virtio: separate allocation of scatter gather list 9p/trans_virtio: turn amount of sg lists into runtime info 9p/trans_virtio: introduce struct virtqueue_sg net/9p: add trans_maxsize to struct p9_client 9p/trans_virtio: support larger msize values 9p/trans_virtio: resize sg lists to whatever is possible net/9p: limit 'msize' to KMALLOC_MAX_SIZE for all transports net/9p: split message size argument into 't_size' and 'r_size' pair 9p: add P9_ERRMAX for 9p2000 and 9p2000.u net/9p: add p9_msg_buf_size() net/9p: allocate appropriate reduced message buffers include/net/9p/9p.h | 3 + include/net/9p/client.h | 2 + net/9p/client.c | 67 +++++++-- net/9p/protocol.c | 154 ++++++++++++++++++++ net/9p/protocol.h | 2 + net/9p/trans_virtio.c | 304 +++++++++++++++++++++++++++++++++++----- 6 files changed, 483 insertions(+), 49 deletions(-) -- 2.30.2