From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 563947D071 for ; Fri, 18 May 2018 17:54:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751458AbeERRy6 (ORCPT ); Fri, 18 May 2018 13:54:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:8267 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751117AbeERRy5 (ORCPT ); Fri, 18 May 2018 13:54:57 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 98EF6300440D; Fri, 18 May 2018 17:54:57 +0000 (UTC) Received: from localhost (ovpn-116-18.gru2.redhat.com [10.97.116.18]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7C03C6091D; Fri, 18 May 2018 17:54:52 +0000 (UTC) Date: Fri, 18 May 2018 14:54:51 -0300 From: Eduardo Habkost To: Paolo Bonzini Cc: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org Subject: Re: [PATCH] kvm: rename HINTS_DEDICATED to KVM_HINTS_REALTIME Message-ID: <20180518175451.GD25013@localhost.localdomain> References: <1526568841-35372-1-git-send-email-mst@redhat.com> <20180517184658.GA1543@localhost.localdomain> <20180517225316-mutt-send-email-mst@kernel.org> <20180518160431.GX25013@localhost.localdomain> <20180518195139-mutt-send-email-mst@kernel.org> <20180518171311.GB25013@localhost.localdomain> <0764c230-3f84-36a5-ad89-fc8dd318d1e4@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0764c230-3f84-36a5-ad89-fc8dd318d1e4@redhat.com> X-Fnord: you can see the fnord User-Agent: Mutt/1.9.2 (2017-12-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Fri, 18 May 2018 17:54:57 +0000 (UTC) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Fri, May 18, 2018 at 07:18:57PM +0200, Paolo Bonzini wrote: > On 18/05/2018 19:13, Eduardo Habkost wrote: > >> As much as we'd like to be helpful and validate input, you need a real > >> time host too. I'm not sure how we'd find out - I suggest we do not > >> bother for now. > > I'm worried that people will start enabling the flag in all kinds > > of scenarios where the guarantees can't be kept, and make the > > meaning of the flag in practice completely different from its > > documented meaning. > > I don't think we should try to detect anything. As far as QEMU is > concerned, it's mostly garbage in, garbage out when it comes to invalid > configurations. It's just a bit, and using it in invalid configurations > is okay if you're doing it (for example) for debugging. In this case, I'd like the requirements and recommendations to be included in QEMU documentation. Especially to point out the most obvious and more likely mistakes (like not ensuring memory is pinned at all, or letting the vCPU threads be interrupted). So, is there a known list of steps required to configure a host to enable kvm-hints-realtime safely, already? I'd like the documentation to be better than "you should fiddle with the CPU affinity on your system and also ensure memory will be pinned; good luck". -- Eduardo -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eduardo Habkost Subject: Re: [PATCH] kvm: rename HINTS_DEDICATED to KVM_HINTS_REALTIME Date: Fri, 18 May 2018 14:54:51 -0300 Message-ID: <20180518175451.GD25013@localhost.localdomain> References: <1526568841-35372-1-git-send-email-mst@redhat.com> <20180517184658.GA1543@localhost.localdomain> <20180517225316-mutt-send-email-mst@kernel.org> <20180518160431.GX25013@localhost.localdomain> <20180518195139-mutt-send-email-mst@kernel.org> <20180518171311.GB25013@localhost.localdomain> <0764c230-3f84-36a5-ad89-fc8dd318d1e4@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <0764c230-3f84-36a5-ad89-fc8dd318d1e4@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Fri, May 18, 2018 at 07:18:57PM +0200, Paolo Bonzini wrote: > On 18/05/2018 19:13, Eduardo Habkost wrote: > >> As much as we'd like to be helpful and validate input, you need a real > >> time host too. I'm not sure how we'd find out - I suggest we do not > >> bother for now. > > I'm worried that people will start enabling the flag in all kinds > > of scenarios where the guarantees can't be kept, and make the > > meaning of the flag in practice completely different from its > > documented meaning. > > I don't think we should try to detect anything. As far as QEMU is > concerned, it's mostly garbage in, garbage out when it comes to invalid > configurations. It's just a bit, and using it in invalid configurations > is okay if you're doing it (for example) for debugging. In this case, I'd like the requirements and recommendations to be included in QEMU documentation. Especially to point out the most obvious and more likely mistakes (like not ensuring memory is pinned at all, or letting the vCPU threads be interrupted). So, is there a known list of steps required to configure a host to enable kvm-hints-realtime safely, already? I'd like the documentation to be better than "you should fiddle with the CPU affinity on your system and also ensure memory will be pinned; good luck". -- Eduardo From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43208) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fJjap-0003fb-Oh for qemu-devel@nongnu.org; Fri, 18 May 2018 13:55:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fJjak-0007Mu-Ti for qemu-devel@nongnu.org; Fri, 18 May 2018 13:55:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54186) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fJjak-0007LI-NK for qemu-devel@nongnu.org; Fri, 18 May 2018 13:54:58 -0400 Date: Fri, 18 May 2018 14:54:51 -0300 From: Eduardo Habkost Message-ID: <20180518175451.GD25013@localhost.localdomain> References: <1526568841-35372-1-git-send-email-mst@redhat.com> <20180517184658.GA1543@localhost.localdomain> <20180517225316-mutt-send-email-mst@kernel.org> <20180518160431.GX25013@localhost.localdomain> <20180518195139-mutt-send-email-mst@kernel.org> <20180518171311.GB25013@localhost.localdomain> <0764c230-3f84-36a5-ad89-fc8dd318d1e4@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0764c230-3f84-36a5-ad89-fc8dd318d1e4@redhat.com> Subject: Re: [Qemu-devel] [PATCH] kvm: rename HINTS_DEDICATED to KVM_HINTS_REALTIME List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org On Fri, May 18, 2018 at 07:18:57PM +0200, Paolo Bonzini wrote: > On 18/05/2018 19:13, Eduardo Habkost wrote: > >> As much as we'd like to be helpful and validate input, you need a real > >> time host too. I'm not sure how we'd find out - I suggest we do not > >> bother for now. > > I'm worried that people will start enabling the flag in all kinds > > of scenarios where the guarantees can't be kept, and make the > > meaning of the flag in practice completely different from its > > documented meaning. > > I don't think we should try to detect anything. As far as QEMU is > concerned, it's mostly garbage in, garbage out when it comes to invalid > configurations. It's just a bit, and using it in invalid configurations > is okay if you're doing it (for example) for debugging. In this case, I'd like the requirements and recommendations to be included in QEMU documentation. Especially to point out the most obvious and more likely mistakes (like not ensuring memory is pinned at all, or letting the vCPU threads be interrupted). So, is there a known list of steps required to configure a host to enable kvm-hints-realtime safely, already? I'd like the documentation to be better than "you should fiddle with the CPU affinity on your system and also ensure memory will be pinned; good luck". -- Eduardo