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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 418EAC433EF for ; Thu, 17 Mar 2022 13:42:35 +0000 (UTC) Received: from localhost ([::1]:38698 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nUqOg-0003CJ-5e for qemu-devel@archiver.kernel.org; Thu, 17 Mar 2022 09:42:34 -0400 Received: from eggs.gnu.org ([209.51.188.92]:52682) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nUqNQ-0002SB-BP for qemu-devel@nongnu.org; Thu, 17 Mar 2022 09:41:16 -0400 Received: from smtp-out1.suse.de ([195.135.220.28]:40880) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1nUqNO-0001Dv-HB for qemu-devel@nongnu.org; Thu, 17 Mar 2022 09:41:16 -0400 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id C937521112; Thu, 17 Mar 2022 13:41:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1647524472; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NGJBxT+xUFsKs+f25LQT45sv6F82JNHuaP7l1JmU9ZM=; b=rTOuOJ4rzGold2quMZdDhafB29BQH2w+go76jxA8zigztjbrOigZIQ1wERHW0l2wkZm+jt VvMAmIzIdb13QLF4VDV5HbrlKKIhDlAInJzmHGF+JZw2puALfGflX7PkwWLDDwtpHO5psZ 8zT5RsGZqzyIN3qYxrPqD7pWy5semMs= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1647524472; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NGJBxT+xUFsKs+f25LQT45sv6F82JNHuaP7l1JmU9ZM=; b=4Ye8ERZ1f7zjJoBIJqX7qmVYlpim1eN8xWbAAtQkEb0/dURkSwWc6QyBX9H7vQf0+lWZJi 9rfWuHjlb/ss7gDg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 9426813BAC; Thu, 17 Mar 2022 13:41:12 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id Xr3pIXg6M2LuFwAAMHmgww (envelope-from ); Thu, 17 Mar 2022 13:41:12 +0000 Subject: Re: [libvirt RFC] virFile: new VIR_FILE_WRAPPER_BIG_PIPE to improve performance To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20220312163001.3811-1-cfontana@suse.de> <34eb53b5-78f7-3814-b71e-aa7ac59f9d25@suse.de> <2d1248d4-ebdf-43f9-e4a7-95f586aade8e@suse.de> <7c641d9d-fffa-e21b-7ae2-12ad35c0c238@suse.de> From: Claudio Fontana Message-ID: Date: Thu, 17 Mar 2022 14:41:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=195.135.220.28; envelope-from=cfontana@suse.de; helo=smtp-out1.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: libvir-list@redhat.com, "Dr. David Alan Gilbert" , qemu-devel Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/17/22 11:25 AM, Daniel P. Berrangé wrote: > On Thu, Mar 17, 2022 at 11:12:11AM +0100, Claudio Fontana wrote: >> On 3/16/22 1:17 PM, Claudio Fontana wrote: >>> On 3/14/22 6:48 PM, Daniel P. Berrangé wrote: >>>> On Mon, Mar 14, 2022 at 06:38:31PM +0100, Claudio Fontana wrote: >>>>> On 3/14/22 6:17 PM, Daniel P. Berrangé wrote: >>>>>> On Sat, Mar 12, 2022 at 05:30:01PM +0100, Claudio Fontana wrote: >>>>>>> the first user is the qemu driver, >>>>>>> >>>>>>> virsh save/resume would slow to a crawl with a default pipe size (64k). >>>>>>> >>>>>>> This improves the situation by 400%. >>>>>>> >>>>>>> Going through io_helper still seems to incur in some penalty (~15%-ish) >>>>>>> compared with direct qemu migration to a nc socket to a file. >>>>>>> >>>>>>> Signed-off-by: Claudio Fontana >>>>>>> --- >>>>>>> src/qemu/qemu_driver.c | 6 +++--- >>>>>>> src/qemu/qemu_saveimage.c | 11 ++++++----- >>>>>>> src/util/virfile.c | 12 ++++++++++++ >>>>>>> src/util/virfile.h | 1 + >>>>>>> 4 files changed, 22 insertions(+), 8 deletions(-) >>>>>>> >>>>>>> Hello, I initially thought this to be a qemu performance issue, >>>>>>> so you can find the discussion about this in qemu-devel: >>>>>>> >>>>>>> "Re: bad virsh save /dev/null performance (600 MiB/s max)" >>>>>>> >>>>>>> https://lists.gnu.org/archive/html/qemu-devel/2022-03/msg03142.html > > >> Current results show these experimental averages maximum throughput >> migrating to /dev/null per each FdWrapper Pipe Size (as per QEMU QMP >> "query-migrate", tests repeated 5 times for each). >> VM Size is 60G, most of the memory effectively touched before migration, >> through user application allocating and touching all memory with >> pseudorandom data. >> >> 64K: 5200 Mbps (current situation) >> 128K: 5800 Mbps >> 256K: 20900 Mbps >> 512K: 21600 Mbps >> 1M: 22800 Mbps >> 2M: 22800 Mbps >> 4M: 22400 Mbps >> 8M: 22500 Mbps >> 16M: 22800 Mbps >> 32M: 22900 Mbps >> 64M: 22900 Mbps >> 128M: 22800 Mbps >> >> This above is the throughput out of patched libvirt with multiple Pipe Sizes for the FDWrapper. > > Ok, its bouncing around with noise after 1 MB. So I'd suggest that > libvirt attempt to raise the pipe limit to 1 MB by default, but > not try to go higher. > >> As for the theoretical limit for the libvirt architecture, >> I ran a qemu migration directly issuing the appropriate QMP >> commands, setting the same migration parameters as per libvirt, >> and then migrating to a socket netcatted to /dev/null via >> {"execute": "migrate", "arguments": { "uri", "unix:///tmp/netcat.sock" } } : >> >> QMP: 37000 Mbps > >> So although the Pipe size improves things (in particular the >> large jump is for the 256K size, although 1M seems a very good value), >> there is still a second bottleneck in there somewhere that >> accounts for a loss of ~14200 Mbps in throughput. > > In the above tests with libvirt, were you using the > --bypass-cache flag or not ? No, I do not. Tests with ramdisk did not show a notable difference for me, but tests with /dev/null were not possible, since the command line is not accepted: # virsh save centos7 /dev/null Domain 'centos7' saved to /dev/null [OK] # virsh save centos7 /dev/null --bypass-cache error: Failed to save domain 'centos7' to /dev/null error: Failed to create file '/dev/null': Invalid argument > > Hopefully use of O_DIRECT doesn't make a difference for > /dev/null, since the I/O is being immediately thrown > away and so ought to never go into I/O cache. > > In terms of the comparison, we still have libvirt iohelper > giving QEMU a pipe, while your test above gives QEMU a > UNIX socket. > > So I still wonder if the delta is caused by the pipe vs socket > difference, as opposed to netcat vs libvirt iohelper code. I'll look into this aspect, thanks! > > With regards, > Daniel > Ciao, Claudio