From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Shishkin Subject: Re: [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace virtualization mode Date: Thu, 3 May 2018 15:02:15 +0300 Message-ID: <20180503120215.dev7ti43zk7yoovn@um.fi.intel.com> References: <1525349323-9938-1-git-send-email-luwei.kang@intel.com> <1525349323-9938-7-git-send-email-luwei.kang@intel.com> <20180503113223.x2ykby6wglppgdwf@um.fi.intel.com> <47494e95-edcb-e8b5-0a32-004e9470dbdf@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Alexander Shishkin , Luwei Kang , kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, rkrcmar@redhat.com, linux-kernel@vger.kernel.org, joro@8bytes.org, peterz@infradead.org, chao.p.peng@linux.intel.com To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <47494e95-edcb-e8b5-0a32-004e9470dbdf@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Thu, May 03, 2018 at 01:50:39PM +0200, Paolo Bonzini wrote: > On 03/05/2018 13:32, Alexander Shishkin wrote: > >> > >> +/* Default is SYSTEM mode. */ > >> +static int __read_mostly pt_mode = PT_MODE_SYSTEM; > >> +module_param(pt_mode, int, S_IRUGO); > > So, it's an explicit module parameter? One apparent problem with this > > is that one would need to reload kvm module(s) to be able to use PT, > > which is not ideal. > > If you want to do tracing system-wide, that by definition must disable > guest tracing, Sure. > so I think the module parameter is appropriate. I don't see why. System-wide tracing takes place while perf record is running. When it's done, it's done and we can un-disable the guest tracing, without requiring the user to kill all their VMs and reload modules. Regards, -- Alex