From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH] KVM: x86: Avoid busy loops over uninjectable pending
 APIC timers
Date: Wed, 20 Mar 2013 23:32:38 +0200
Message-ID: <20130320213238.GB9382@redhat.com>
References: <5144DAC3.7080401@web.de>
 <20130317084705.GC11223@redhat.com>
 <51459ECE.2000107@web.de>
 <20130317104717.GA6117@redhat.com>
 <20130320193033.GB11138@amt.cnet>
 <20130320200319.GA16367@amt.cnet>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Yang Zhang <yang.z.zhang@Intel.com>,
	Jan Kiszka <jan.kiszka@web.de>, kvm <kvm@vger.kernel.org>
To: Marcelo Tosatti <mtosatti@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:23231 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751242Ab3CTVcp (ORCPT <rfc822;kvm@vger.kernel.org>);
	Wed, 20 Mar 2013 17:32:45 -0400
Content-Disposition: inline
In-Reply-To: <20130320200319.GA16367@amt.cnet>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Wed, Mar 20, 2013 at 05:03:19PM -0300, Marcelo Tosatti wrote:
> On Wed, Mar 20, 2013 at 04:30:33PM -0300, Marcelo Tosatti wrote:
> > On Sun, Mar 17, 2013 at 12:47:17PM +0200, Gleb Natapov wrote:
> > > On Sun, Mar 17, 2013 at 11:45:34AM +0100, Jan Kiszka wrote:
> > > > On 2013-03-17 09:47, Gleb Natapov wrote:
> > > > > On Sat, Mar 16, 2013 at 09:49:07PM +0100, Jan Kiszka wrote:
> > > > >> From: Jan Kiszka <jan.kiszka@siemens.com>
> > > > >>
> > > > >> If the guest didn't take the last APIC timer interrupt yet and generates
> > > > >> another one on top, e.g. via periodic mode, we do not block the VCPU
> > > > >> even if the guest state is halted. The reason is that
> > > > >> apic_has_pending_timer continues to return a non-zero value.
> > > > >>
> > > > >> Fix this busy loop by taking the IRR content for the LVT vector in
> > > > >> apic_has_pending_timer into account.
> > > > >>
> > > > > Just drop coalescing tacking for lapic interrupt. After posted interrupt
> > > > > will be merged __apic_accept_irq() will not longer return coalescing
> > > > > information, so the code will be dead anyway.
> > > > 
> > > > That requires the RTC decoalescing series to go first to avoid a
> > > > regression, no? Then let's postpone this topic for now.
> > > > 
> > > Yes, but decoalescing will work only for RTC :(
> > 
> > Are you proposing to drop LAPIC interrupt reinjection? 
> 
> Since timer handling and injection is VCPU-local for LAPIC,
> __apic_accept_irq can (and must) return coalesced information (cannot
> drop LAPIC interrupt reinjection).
> 
Why can't we drop LAPIC interrupt reinjection? Proposed posted interrupt
patches do not properly check for interrupt coalescing even for
VCPU-local injection.

--
			Gleb.