From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eduardo Habkost Subject: Re: [RFC] kvm: x86: export vCPU halted state to sysfs Date: Fri, 2 Feb 2018 13:25:32 -0200 Message-ID: <20180202152532.GL26425@localhost.localdomain> References: <20180201125441.2f5b4fdd@redhat.com> <20180201201514.GB660@flask> <20180201202649.GG26425@localhost.localdomain> <20180202141554.GH26425@localhost.localdomain> <20180202141938.GJ15403@redhat.com> <20180202092159.48d9bd4c@redhat.com> <20180202145014.GI26425@localhost.localdomain> <20180202150718.GL15403@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Cc: Luiz Capitulino , Viktor Mihajlovski , Radim =?utf-8?B?S3LEjW3DocWZ?= , kvm@vger.kernel.org, pbonzini@redhat.com, Peter Krempa , John Ferlan , libvir-list@redhat.com, Christian Borntraeger , qemu-devel@nongnu.org, Markus Armbruster , Eric Blake To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Return-path: Received: from mx1.redhat.com ([209.132.183.28]:37030 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751735AbeBBPZm (ORCPT ); Fri, 2 Feb 2018 10:25:42 -0500 Content-Disposition: inline In-Reply-To: <20180202150718.GL15403@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, Feb 02, 2018 at 03:07:18PM +0000, Daniel P. Berrangé wrote: > On Fri, Feb 02, 2018 at 12:50:14PM -0200, Eduardo Habkost wrote: > > (CCing qemu-devel) > > > > On Fri, Feb 02, 2018 at 09:21:59AM -0500, Luiz Capitulino wrote: > > > On Fri, 2 Feb 2018 14:19:38 +0000 > > > Daniel P. Berrangé wrote: > > > > On Fri, Feb 02, 2018 at 12:15:54PM -0200, Eduardo Habkost wrote: > > [...] > > > > > It would be also interesting to update QEMU QMP documentation to > > > > > clarify the arch-specific semantics of "halted". > > > > > > > > Any also especially clarify the awful performance implications of running > > > > this particular query command. In general I would not expect query-xxx > > > > monitor commands to interrupt all vcpus, so we should clearly warn about > > > > this ! > > > > > > Or deprecate it... > > > > We could deprecate the expensive fields on query-cpus, and move > > them to a more expensive query-cpu-state command. I believe most > > users of query-cpus are only interested in qom_path, thread_id, > > and topology info. > > > > Markus, Eric: from the QAPI point of view, is it OK to remove > > fields between QEMU versions, as long as we follow our > > deprecation policy? > > I would expect that to not be OK. A fully backwards compatible way to > deal with this would just be to add a flag to the query-cpus command > eg something like > > query-cpus arch-specific=false > > to turn off all this arch specific state, and just report the cheap > generic info. If it defaults to arch-specific=true when omitted, then > there's no compat problems. This would work, too. I would name it "full-state", "extended-state" or something similar, though. Not all arch-specific data is expensive to fetch, and not all non-arch-specific data is unexpensive. But I'd like to confirm if it's OK to make existing non-optional struct fields optional in the QAPI schema. Markus, Eric? -- Eduardo