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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 7FB39C43331 for ; Thu, 26 Mar 2020 10:12:17 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 544EC2070A for ; Thu, 26 Mar 2020 10:12:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 544EC2070A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jHPUS-0004BD-I3; Thu, 26 Mar 2020 10:11:56 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jHPUQ-0004B8-Mn for xen-devel@lists.xenproject.org; Thu, 26 Mar 2020 10:11:54 +0000 X-Inumbo-ID: 3757b188-6f4a-11ea-bec1-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 3757b188-6f4a-11ea-bec1-bc764e2007e4; Thu, 26 Mar 2020 10:11:54 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id F3CC0AF57; Thu, 26 Mar 2020 10:11:52 +0000 (UTC) To: Jan Beulich References: <20200326094557.13822-1-jgross@suse.com> <574ad265-7b49-6a60-fa74-655d81593049@suse.com> <5ecfa9a2-32f1-cac5-da33-842a3e13a01f@suse.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: <3760678b-62b0-cced-0a7a-61ea2f874294@suse.com> Date: Thu, 26 Mar 2020 11:11:52 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [Xen-devel] [PATCH] tools/libxl: make default of max event channels dependant on vcpus X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Anthony PERARD , xen-devel@lists.xenproject.org, Ian Jackson , Wei Liu Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 26.03.20 11:05, Jan Beulich wrote: > On 26.03.2020 11:00, Jürgen Groß wrote: >> On 26.03.20 10:54, Jan Beulich wrote: >>> On 26.03.2020 10:45, Juergen Gross wrote: >>>> Today the maximum number of event channels for a guest is defaulting >>>> to 1023. For large guests with lots of vcpus this is not enough, as >>>> e.g. the Linux kernel uses 7 event channels per vcpu, limiting the >>>> guest to about 140 vcpus. >>> >>> I don't think any particular guest OS should "dictate" the default >>> here. What if another OS (or even a future version of Linux) requires >>> more than 8? And why would the value depend on number of vCPU-s but >>> not number and kind of virtual devices? >> >> It is a rough estimate. And with HVM guests being limited to 128 cpus >> anyway, this problem is more relevant for PV guests, limiting the >> available options for guest OS's. > > How many evtchns would e.g. mini-os require? I.e. wouldn't such stubdoms > get a much larger than necessary allowance this way? mini-os doesn't support SMP. So (if not configured with lots of vcpus, which doesn't make sense) they still get 1023 event channels per default. Which is much more as they need, but the same as today. Xenstore stubdom is unlimited like dom0, BTW. Juergen