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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 0E5DBC33C9E for ; Thu, 30 Jan 2020 11:04:30 +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 CB11D206F0 for ; Thu, 30 Jan 2020 11:04:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EWj2tgNZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CB11D206F0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58646 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ix7cb-0006xa-14 for qemu-devel@archiver.kernel.org; Thu, 30 Jan 2020 06:04:29 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:50504) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ix7bz-0006Ts-Tc for qemu-devel@nongnu.org; Thu, 30 Jan 2020 06:03:53 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ix7by-0002Ie-5o for qemu-devel@nongnu.org; Thu, 30 Jan 2020 06:03:51 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:32353 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ix7by-0002II-1e for qemu-devel@nongnu.org; Thu, 30 Jan 2020 06:03:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580382229; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ysnc02IrGZRr75lRD5Y5zD8LkutuR6ZXlRHRWGANGd4=; b=EWj2tgNZ6dXmpyWjik2A67hZnRcXLcME1zzHqMOvQPmVFqjQa/waDNt+xS5KZCzvrt4KwG 2Zmz6fWiVYRp96T2BnUoufb0V9FwKB/gyrLAx1eaWfl8vHsUxfjxPZs/Vu0w5gTdqADdDz maWjMPX0JE6ZOyipaej3+viOmiJIpGU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-314-NE4-rVvoMlSI66JRnuN1rw-1; Thu, 30 Jan 2020 06:03:47 -0500 X-MC-Unique: NE4-rVvoMlSI66JRnuN1rw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 052C4100551D; Thu, 30 Jan 2020 11:03:46 +0000 (UTC) Received: from gondolin (ovpn-117-199.ams2.redhat.com [10.36.117.199]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3DD6B5C1B2; Thu, 30 Jan 2020 11:03:38 +0000 (UTC) Date: Thu, 30 Jan 2020 12:03:14 +0100 From: Cornelia Huck To: Stefan Hajnoczi Subject: Re: [PATCH v2 2/4] virtio-scsi: default num_queues to -smp N Message-ID: <20200130120314.5d4ad113.cohuck@redhat.com> In-Reply-To: <20200130105235.GC176651@stefanha-x1.localdomain> References: <20200124100159.736209-1-stefanha@redhat.com> <20200124100159.736209-3-stefanha@redhat.com> <20200127141031.6e108839.cohuck@redhat.com> <20200129154438.GC157595@stefanha-x1.localdomain> <20200130105235.GC176651@stefanha-x1.localdomain> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; boundary="Sig_/dYAYDJttwU6UCIo+vbbte=D"; protocol="application/pgp-signature"; micalg=pgp-sha256 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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: , Cc: Kevin Wolf , Fam Zheng , Eduardo Habkost , qemu-block@nongnu.org, "Michael S. Tsirkin" , Stefan Hajnoczi , qemu-devel@nongnu.org, Max Reitz , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --Sig_/dYAYDJttwU6UCIo+vbbte=D Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Thu, 30 Jan 2020 10:52:35 +0000 Stefan Hajnoczi wrote: > On Thu, Jan 30, 2020 at 01:29:16AM +0100, Paolo Bonzini wrote: > > On 29/01/20 16:44, Stefan Hajnoczi wrote: =20 > > > On Mon, Jan 27, 2020 at 02:10:31PM +0100, Cornelia Huck wrote: =20 > > >> On Fri, 24 Jan 2020 10:01:57 +0000 > > >> Stefan Hajnoczi wrote: =20 > > >>> @@ -47,10 +48,15 @@ static void vhost_scsi_pci_realize(VirtIOPCIPro= xy *vpci_dev, Error **errp) > > >>> { > > >>> VHostSCSIPCI *dev =3D VHOST_SCSI_PCI(vpci_dev); > > >>> DeviceState *vdev =3D DEVICE(&dev->vdev); > > >>> - VirtIOSCSICommon *vs =3D VIRTIO_SCSI_COMMON(vdev); > > >>> + VirtIOSCSIConf *conf =3D &dev->vdev.parent_obj.parent_obj.conf= ; > > >>> + > > >>> + /* 1:1 vq to vcpu mapping is ideal because it avoids IPIs */ > > >>> + if (conf->num_queues =3D=3D VIRTIO_SCSI_AUTO_NUM_QUEUES) { > > >>> + conf->num_queues =3D current_machine->smp.cpus; =20 > > >> This now maps the request vqs 1:1 to the vcpus. What about the fixed > > >> vqs? If they don't really matter, amend the comment to explain that?= =20 > > > The fixed vqs don't matter. They are typically not involved in the d= ata > > > path, only the control path where performance doesn't matter. =20 > >=20 > > Should we put a limit on the number of vCPUs? For anything above ~128 > > the guest is probably not going to be disk or network bound. =20 >=20 > Michael Tsirkin pointed out there's a hard limit of VIRTIO_QUEUE_MAX > (1024). We need to at least stay under that limit. >=20 > Should the guest have >128 virtqueues? Each virtqueue requires guest > RAM and 2 host eventfds. Eventually these resource requirements will > become a scalability problem, but how do we choose a hard limit and what > happens to guest performance above that limit? There's probably two kind of limits involved here: - a hard limit (we cannot do more), which should be checked even for user-specified values, and - a soft limit (it does not make sense to go beyond this for the default case), which can be overridden if explicitly specified. VIRTIO_QUEUE_MAX (and two less for virtio-scsi) sounds like a hard limit, maybe 128 is a reasonable candidate for a soft limit. (I would expect systems that give 128 vcpus to the guest to also be generously sized in other respects.) --Sig_/dYAYDJttwU6UCIo+vbbte=D Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEw9DWbcNiT/aowBjO3s9rk8bwL68FAl4yt/IACgkQ3s9rk8bw L68v4RAAmNONBZ1RD8SLGd/vXUVfCPrC/t7kcCowzTq2BKRlJAHEHGm9q4Afsv/r 9Ndd9I13FmoxRhsXe6OuSvCQbdUAgY5qyT6DNFc33SrhVYsyrVX7eWEJYs4Ywscf Wtrk3Vz0bfvSvZsrmuJOTOPOVxa7fzJZFyLZV3qDcOEshcSF/MUtyQ+4T+soZ4xI HYMP4DdtjCdwaJsFcEQul3hODwdsJo0t18yaXtbHFoLgYHYpA8H2EKyO7DDtOp3l yspinJUwp3eEfAm8Tt+//6RyCi6PTqPRONpbMcM2tXnDcqL1gDJOgZtMkorWZFfi C6kOAUum9bWP92cYZ36XwBhxlgLBhaOwpSGOl4/CmTBTLikaSeMl1XaqKG/ALxnY A3DpIdi9lgW7OfXaFXPkQO1YJRU6IpWHiMzrFIcyU/S+gvlW/mgleiRHrWra2vap 4wI7Tg80jiVgwDtc9QdKdp3G6n4q/GdP9S0qJcmI+LW07hKdKPnHnrFio4LrpZFe BQA4CBq6QYgiS910o8cW8jCnDFSi3enTwgSFCRzoARUrDJianvYSecNnrSI6UUA2 tdOw4RkMjqehOWH7ATVE7Q5CFcjTkjrVjTOliRFQnk/TIsmbJyiz+nuxmrO+kiRM DS4+1NQoI0G6iFK6rEnh7kNC4KzjqSqvC0O1zU/3q1UujMmtssI= =qyla -----END PGP SIGNATURE----- --Sig_/dYAYDJttwU6UCIo+vbbte=D--