From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752383AbdBNSiW (ORCPT <rfc822;w@1wt.eu>);
        Tue, 14 Feb 2017 13:38:22 -0500
Received: from bombadil.infradead.org ([65.50.211.133]:51063 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1752005AbdBNSiP (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 14 Feb 2017 13:38:15 -0500
Date: Tue, 14 Feb 2017 19:38:07 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        vince@deater.net, eranian@google.com,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Borislav Petkov <bp@suse.de>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 1/2] perf/x86/intel/pt: Fail event scheduling on conflict
 with VMX
Message-ID: <20170214183807.GT6500@twins.programming.kicks-ass.net>
References: <20170214132416.26400-1-alexander.shishkin@linux.intel.com>
 <20170214132416.26400-2-alexander.shishkin@linux.intel.com>
 <20170214135620.GN6500@twins.programming.kicks-ass.net>
 <87d1eklpb9.fsf@ashishki-desk.ger.corp.intel.com>
 <20170214162702.GR6500@twins.programming.kicks-ass.net>
 <874lzwlmch.fsf@ashishki-desk.ger.corp.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <874lzwlmch.fsf@ashishki-desk.ger.corp.intel.com>
User-Agent: Mutt/1.5.23.1 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Feb 14, 2017 at 07:21:34PM +0200, Alexander Shishkin wrote:
> Peter Zijlstra <peterz@infradead.org> writes:
> 
> > On Tue, Feb 14, 2017 at 06:17:30PM +0200, Alexander Shishkin wrote:
> >> This is called by pmu::add(), which checks hw.state afterwards and if it
> >> finds HES_STOPPED, it returns an error, which event_sched_in() captures
> >> and keeps the event in INACTIVE state. Should I add a comment about it?
> >
> > Egads... so what if ->add() succeeds but we then hit this on
> > ->stop()/->start() due to throttle or period adjust?
> 
> It will hang there with hw.state==PERF_HES_STOPPED till the next
> sched_out. But that will be the case anyway if VMXON kicks in while PT
> is running.

Right, so I question the whole 'lets not schedule PT when VMX' premise,
it leads to inconsistencies all over. How about we treat it like
->add() succeeded and VMX simply results in no output.

Esp. when you then emit 'fake' data into/from a vmlaunch/vmresume
instruction.