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 mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E6FEC433EF for ; Tue, 14 Dec 2021 10:34:02 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 2D5454B1AB; Tue, 14 Dec 2021 05:34:02 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Authentication-Results: mm01.cs.columbia.edu (amavisd-new); dkim=softfail (fail, message has been altered) header.i=@kernel.org Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id AMAE0sgR8S4i; Tue, 14 Dec 2021 05:34:01 -0500 (EST) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 2EA054B18F; Tue, 14 Dec 2021 05:34:01 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 82FAB4B18F for ; Tue, 14 Dec 2021 05:33:59 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 7h6yKqnDY-lK for ; Tue, 14 Dec 2021 05:33:58 -0500 (EST) Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 38D2F4B15B for ; Tue, 14 Dec 2021 05:33:58 -0500 (EST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id F3D8261343; Tue, 14 Dec 2021 10:33:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5969CC34600; Tue, 14 Dec 2021 10:33:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639478036; bh=3ia3rGv+6KKb/qFcaFJr2fBE/lbWtHfOzjwbdJoPYUc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Cg5zBOBc7TeFArMWkx5K7JGIZVvvmPlbwf0kBQI6/2GwMZVhfmaMQomALfKUBuKnT w3KA9Gn9hdS/iB6EvVuW22BXOTOUDftFBiPRQ8kodY8SbZwL5Ne7Ud25SGr6ixtj63 KxJIFg3VjlJeGQ4tq5VHCgPppLx0g86LCLARxfSj7r2NWfKQpbdmA941f9trF8iORS fGubwiJfS9+JGhtVIkpkT6pZeQCy3auzCZs8ibH7PTAadCO71mjDXwWC06ky3dpCZ9 X9FQ61cEalXhPFz/bliKt4ntIWogFLj7XmVWSBsE+97X3MV0EuU5/yNd8e8SYrlOKn ciXc3OD0g80Nw== Received: from cfbb000407.r.cam.camfibre.uk ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mx586-00C1KI-Fz; Tue, 14 Dec 2021 10:33:54 +0000 Date: Tue, 14 Dec 2021 10:33:53 +0000 Message-ID: <87bl1jjx0u.wl-maz@kernel.org> From: Marc Zyngier To: Peter Maydell Subject: Re: Libvirt on little.BIG ARM systems unable to start guest if no cpuset is provided In-Reply-To: References: <70a2f7d6-5ac1-72df-4a88-b1a662d07070@gmx.com> <32bb61a9-0938-d254-0453-18a108bc4b63@redhat.com> <1dc0403b-c61b-b04b-e7fd-f2d66276ba7b@gmx.com> <87lf0ojvq2.wl-maz@kernel.org> <29409a18-5156-6b3a-6a44-eecd83a20a78@redhat.com> <2281a255-fef3-c872-963e-2c5274d0d815@gmx.com> <87ee6fjyyh.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: peter.maydell@linaro.org, quwenruo.btrfs@gmx.com, mprivozn@redhat.com, libvirt-users@redhat.com, qemu-arm@nongnu.org, kvmarm@lists.cs.columbia.edu, qemu-discuss@nongnu.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: Michal =?UTF-8?B?UHLDrXZvem7DrWs=?= , Qu Wenruo , qemu-discuss@nongnu.org, libvirt-users@redhat.com, qemu-arm@nongnu.org, kvmarm X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Tue, 14 Dec 2021 10:08:29 +0000, Peter Maydell wrote: > > On Tue, 14 Dec 2021 at 09:52, Marc Zyngier wrote: > > The best workaround is to taskset the QEMU process (and I really mean > > the process, not individual threads) to an homogeneous set of CPUs and > > be done with it. > > Agreed. I suspect that often the 'little' CPUs are sufficiently > low-power to probably not be worth giving to the VM anyway. They are actually pretty beefy, in most cases. If you are I/O bound, the small cores are the right target. This email is brought to you via a couple of A55 CPUs running a VM and acting as my home gateway. If 'the internet' was getting slow, I'd have heard about it! ;-) > Side note: if you *do* give a guest both big and little CPUs > using kvmtool or something similar, does the guest kernel get > enough information to schedule tasks properly to both kinds of > CPU, or does it just assume they're all the same and happily > put performance-requiring tasks on the little CPUs ? Upstream kvmtool doesn't make any effort to do this, but I had a series to perform such placement in the past. Once you know which physical CPUs you are placing the vcpus on, you can extract the individual CPU capacity[1] and expose it in the guest's DT as a cpu-specific 'capacity-dmips-mhz' property. A Linux guest will take the hint and do the right thing. M. [1] /sys/devices/system/cpu/cpu*/cpu_capacity -- Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm