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 8B61EC43331 for ; Thu, 26 Mar 2020 10:06:19 +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 631E32070A for ; Thu, 26 Mar 2020 10:06:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 631E32070A 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 1jHPOh-0003Gh-Nr; Thu, 26 Mar 2020 10:05:59 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1jHPOg-0003Gc-O8 for xen-devel@lists.xenproject.org; Thu, 26 Mar 2020 10:05:58 +0000 X-Inumbo-ID: 60b01aa9-6f49-11ea-8798-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 60b01aa9-6f49-11ea-8798-12813bfff9fa; Thu, 26 Mar 2020 10:05:53 +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 EB8A5AF57; Thu, 26 Mar 2020 10:05:52 +0000 (UTC) To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= References: <20200326094557.13822-1-jgross@suse.com> <574ad265-7b49-6a60-fa74-655d81593049@suse.com> <5ecfa9a2-32f1-cac5-da33-842a3e13a01f@suse.com> From: Jan Beulich Message-ID: Date: Thu, 26 Mar 2020 11:05:52 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <5ecfa9a2-32f1-cac5-da33-842a3e13a01f@suse.com> Content-Type: text/plain; charset=utf-8 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 26.03.2020 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? Jan