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 99E11C7EE2C for ; Fri, 2 Jun 2023 09:45:36 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1q51LF-0004VE-0g; Fri, 02 Jun 2023 05:45:05 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1q51LC-0004Uz-GA for qemu-devel@nongnu.org; Fri, 02 Jun 2023 05:45:02 -0400 Received: from mail-wm1-x331.google.com ([2a00:1450:4864:20::331]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1q51LA-00029Y-Li for qemu-devel@nongnu.org; Fri, 02 Jun 2023 05:45:02 -0400 Received: by mail-wm1-x331.google.com with SMTP id 5b1f17b1804b1-3f6e68cc738so17847555e9.1 for ; Fri, 02 Jun 2023 02:45:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1685699099; x=1688291099; h=content-transfer-encoding:mime-version:message-id:in-reply-to:date :subject:cc:to:from:user-agent:references:from:to:cc:subject:date :message-id:reply-to; bh=v9Fmeskjd8My9ulf4PrEVJeJh8p34sKN80rfH53l5u8=; b=tuyj8MPfPHGh0c0eLy9GZ5X0THgWuKdJbyVMTxxaQgpYgmmGxtUwIJnHWN7buo09xe uo/l7EvF4YQJ4wPmMqEOG07+CGF3kOPprs+994VEmz5QDRiWSvUeEtE8lqmHOp/oONJR Zcy0RUsyfMbFsIxZYNRxC5jOna7w5nwBM5PW8oCrs8aurhHdasPZj/i1pcQQ4Ex4V4T5 k9AgxPX5YiR65DbWfrCuat9+WYZdHh/9HMruJ4TIoMEzB1wbsuYtlnmTBd72Mx0/o2CA hMdenUS4fM4H9Ngc53/CGB1hLEC3H/lrf7KAAj4jwEzwC15MHlvakJIRQGQeam0DmccT qYBA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685699099; x=1688291099; h=content-transfer-encoding:mime-version:message-id:in-reply-to:date :subject:cc:to:from:user-agent:references:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=v9Fmeskjd8My9ulf4PrEVJeJh8p34sKN80rfH53l5u8=; b=Z1lEkMoPKJ3+SQ9c1h6jYH135wlg0aR+gleeTNj4+vrjYMkDDkL+qM84iuFkcOZAFB uwSLq4eSx0+Lbrm9PHnsd+0ddqmPR4+PsIOzVFb0Gou93w6++KlJYp/bYiK/zLI3n6LG BvsEmlPFzUpgyLAlaxhIfwbrZ5mW0BdJHQXFptDHcOZO15e0+CMkxrlOId9riKYrne3S Bs71nebQEujRDi0E86iCm51CWSpZVeMY5kg0zyzmyDS/XtjpGexO0ePi+NJfPcaeW2aS zTyISqWPvPJQaNHYRwUTJEDtyJLOetAn36zAeCu6wGYFgceo/+FihxcPwIRI2XdrlsWe vU0w== X-Gm-Message-State: AC+VfDw+t01dxVspPtKicuSGTNCPOraHafJ5D+3egQLCl7pCH+Px+NHs jfXQ8jnLfy4wCpK98/b2ixuDsw== X-Google-Smtp-Source: ACHHUZ5e69hBrZlQM9Ekgsqo7q5a8VsHwhv5LH7jGi9pRo9cs0QQVjIx+J+Rjoxw0KPzktVf9CnNVA== X-Received: by 2002:a05:600c:289:b0:3f6:3bb:5135 with SMTP id 9-20020a05600c028900b003f603bb5135mr1490900wmk.14.1685699098987; Fri, 02 Jun 2023 02:44:58 -0700 (PDT) Received: from zen.linaroharston ([85.9.250.243]) by smtp.gmail.com with ESMTPSA id j9-20020a5d5649000000b0030b5d203e7esm1121477wrw.97.2023.06.02.02.44.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Jun 2023 02:44:58 -0700 (PDT) Received: from zen (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id 0D4821FFBB; Fri, 2 Jun 2023 10:44:58 +0100 (BST) References: <87y1l2rixp.fsf@secure.mitica> User-agent: mu4e 1.11.6; emacs 29.0.91 From: Alex =?utf-8?Q?Benn=C3=A9e?= To: Peter Maydell Cc: =?utf-8?Q?Daniel_P=2E_Berrang=C3=A9?= , Juan Quintela , Richard Henderson , qemu-devel@nongnu.org Subject: Re: Big TCG slowdown when using zstd with aarch64 Date: Fri, 02 Jun 2023 10:42:26 +0100 In-reply-to: Message-ID: <877csmb3l2.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::331; envelope-from=alex.bennee@linaro.org; helo=mail-wm1-x331.google.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, RCVD_IN_DNSWL_NONE=-0.0001, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Peter Maydell writes: > On Fri, 2 Jun 2023 at 10:10, Daniel P. Berrang=C3=A9 wrote: >> I suspect that the zstd logic takes a little bit longer in setup, >> which allows often allows the guest dirty workload to get ahead of >> it, resulting in a huge amount of data to transfer. Every now and >> then the compression code gets ahead of the workload and thus most >> data is zeros and skipped. >> >> IMHO this feels like just another example of compression being largely >> useless. The CPU overhead of compression can't keep up with the guest >> dirty workload, making the supposedly network bandwidth saving irrelevan= t. > > It seems a bit surprising if compression can't keep up with > a TCG guest workload, though... Actual running code doesn't see much of a look in on the perf data: 4.17% CPU 0/TCG qemu-system-aarch64 [.] tlb_set_dirty 3.55% CPU 0/TCG qemu-system-aarch64 [.] helper_ldub_mmu 1.58% live_migration qemu-system-aarch64 [.] buffer_zero_avx2 1.35% CPU 0/TCG qemu-system-aarch64 [.] tlb_set_page_full 1.11% multifdsend_2 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.07% multifdsend_13 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.07% multifdsend_6 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.07% multifdsend_8 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.06% multifdsend_10 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.06% multifdsend_3 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.05% multifdsend_7 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.04% multifdsend_11 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.04% multifdsend_15 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.04% multifdsend_9 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.03% multifdsend_1 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.03% multifdsend_0 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.02% multifdsend_4 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.02% multifdsend_14 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.02% multifdsend_12 libc.so.6 [.] __memmove_avx_unali= gned_erms 1.01% multifdsend_5 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.96% multifdrecv_3 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.94% multifdrecv_13 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.94% multifdrecv_2 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.93% multifdrecv_15 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.93% multifdrecv_10 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.93% multifdrecv_12 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.92% multifdrecv_0 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.92% multifdrecv_1 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.92% multifdrecv_8 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.91% multifdrecv_6 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.91% multifdrecv_7 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.91% multifdrecv_4 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.91% multifdrecv_11 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.90% multifdrecv_14 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.90% multifdrecv_5 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.89% multifdrecv_9 libc.so.6 [.] __memmove_avx_unali= gned_erms 0.77% CPU 0/TCG qemu-system-aarch64 [.] cpu_physical_memory= _get_dirty.constprop.0 0.59% migration-test [kernel.vmlinux] [k] syscall_exit_to_use= r_mode 0.55% multifdrecv_12 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.54% multifdrecv_4 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.51% multifdrecv_5 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.51% multifdrecv_14 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.49% multifdrecv_2 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.45% multifdrecv_1 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.45% multifdrecv_9 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.42% multifdrecv_10 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.40% multifdrecv_6 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.40% multifdrecv_3 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.40% multifdrecv_8 libzstd.so.1.5.4 [.] 0x000000000008ec20 0.39% multifdrecv_7 libzstd.so.1.5.4 [.] 0x000000000008ec20 > > -- PMM --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro