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=-8.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 A03D9C64E7C for ; Wed, 2 Dec 2020 16:35:24 +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 2EEE920872 for ; Wed, 2 Dec 2020 16:35:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2EEE920872 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=citrix.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.42882.77172 (Exim 4.92) (envelope-from ) id 1kkV5t-0007PF-6t; Wed, 02 Dec 2020 16:35:05 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 42882.77172; Wed, 02 Dec 2020 16:35:05 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kkV5t-0007P8-3E; Wed, 02 Dec 2020 16:35:05 +0000 Received: by outflank-mailman (input) for mailman id 42882; Wed, 02 Dec 2020 16:35:04 +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 4.92) (envelope-from ) id 1kkV5s-0007P3-0a for xen-devel@lists.xenproject.org; Wed, 02 Dec 2020 16:35:04 +0000 Received: from esa2.hc3370-68.iphmx.com (unknown [216.71.145.153]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 896997d7-e286-4c90-bb7d-f0d01f8bb686; Wed, 02 Dec 2020 16:35:02 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 896997d7-e286-4c90-bb7d-f0d01f8bb686 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=citrix.com; s=securemail; t=1606926902; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=eycOKdvUo1CyiWQtNu/Nm7EaPdWQhjbeuuRaBlXKR4Q=; b=IwjzciYoSicWztxaIM9IauZHGhQn/8xBxj+mDss26ZRmR/3tX4ia3W2j 0UwB1lnsIJ28fGaY/2Y3v5bEGArK2YN3MFJUgyeFGoFOUFvUGu2CyKPt2 CXVPhsqoyMpVHBDOljORiTUWLsdGmC9d2V1gl7GijfLq+E6a284FMcs7J o=; Authentication-Results: esa2.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none IronPort-SDR: 1NQUARUK5eMmTpNbHwSkFWjmAQc3uAN53dEqKAZZMYHmVQMxFAuCg0+idIP1f0TjWD9xsgjS7m gs77VQH+9dNT8lEgv/Oe9gQQIkpe7VhWlIvLXKdlTsTBa7pbbbAIgM7TFeYl/gzdvOiylRfsFq K9ATtHRtZIIuE4RsapGHA739VflB95/4VSx8ungxV/HUrbpC3U8hoSIv6YUB/Ql+PxfewVmpKo LgNR0hGGQnK1QhepEKlH0k8TSqMadXLC2DDqMpYzRGzgTx7118B7dE/T8DViJEdNDFT6H/Mclz YR0= X-SBRS: None X-MesageID: 32376019 X-Ironport-Server: esa2.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.78,387,1599537600"; d="scan'208";a="32376019" Subject: Re: [PATCH] x86/IRQ: bump max number of guests for a shared IRQ to 31 To: Jan Beulich CC: , , , References: <1606780777-30718-1-git-send-email-igor.druzhinin@citrix.com> <3c9735ec-2b04-1ace-2adb-d72b32c4a5f9@citrix.com> <88019c81-1988-2512-282b-53b61adf09c6@suse.com> From: Igor Druzhinin Message-ID: Date: Wed, 2 Dec 2020 16:34:55 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <88019c81-1988-2512-282b-53b61adf09c6@suse.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit On 02/12/2020 15:21, Jan Beulich wrote: > On 02.12.2020 15:53, Igor Druzhinin wrote: >> On 02/12/2020 09:25, Jan Beulich wrote: >>> Instead I'm wondering whether this wouldn't better be a Kconfig >>> setting (or even command line controllable). There don't look to be >>> any restrictions on the precise value chosen (i.e. 2**n-1 like is >>> the case for old and new values here, for whatever reason), so a >>> simple permitted range of like 4...64 would seem fine to specify. >>> Whether the default then would want to be 8 (close to the current >>> 7) or higher (around the actually observed maximum) is a different >>> question. >> >> I'm in favor of a command line argument here - it would be much less trouble >> if a higher limit was suddenly necessary in the field. The default IMO >> should definitely be higher than 8 - I'd stick with number 32 which to me >> should cover our real world scenarios and apply some headroom for the future. > > Well, I'm concerned of the extra memory overhead. Every IRQ, > sharable or not, will get the extra slots allocated with the > current scheme. Perhaps a prereq change then would be to only > allocate multi-guest arrays for sharable IRQs, effectively > shrinking the overhead in particular for all MSI ones? That's one way to improve overall system scalability but in that area there is certainly much bigger fish to fry elsewhere. With 32 elements in the array we get 200 bytes of overhead per structure, with 16 it's just 72 extra bytes which in the unattainable worst case scenario of every single vector taken in 512 CPU machine would only account for several MB of overhead. I'd start with dynamic array allocation first and setting the limit to 16 that should be enough for now. And then if that default value needs to be raised we can consider further improvements. Igor