From: Marcelo Tosatti <mtosatti@redhat.com>
To: Gleb Natapov <gleb@redhat.com>
Cc: Yang Zhang <yang.z.zhang@Intel.com>,
Jan Kiszka <jan.kiszka@web.de>, kvm <kvm@vger.kernel.org>
Subject: Re: [PATCH] KVM: x86: Avoid busy loops over uninjectable pending APIC timers
Date: Thu, 21 Mar 2013 11:02:24 -0300 [thread overview]
Message-ID: <20130321140224.GA29237@amt.cnet> (raw)
In-Reply-To: <20130321045446.GC9382@redhat.com>
On Thu, Mar 21, 2013 at 06:54:46AM +0200, Gleb Natapov wrote:
> On Wed, Mar 20, 2013 at 08:19:13PM -0300, Marcelo Tosatti wrote:
> > On Wed, Mar 20, 2013 at 11:32:38PM +0200, Gleb Natapov wrote:
> > > 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.
> >
> > Because older Linux guests depend on reinjection for proper timekeeping.
> Which versions? Those without kvmclock? Can we make them use PIT instead?
> Posted interrupts going to break them.
There is no reason to break them if its OK to receive reinjection info
from LAPIC... its a matter of returning the information from
apic_accept_irq, no big deal.
next prev parent reply other threads:[~2013-03-21 14:02 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-16 20:49 [PATCH] KVM: x86: Avoid busy loops over uninjectable pending APIC timers Jan Kiszka
2013-03-17 8:47 ` Gleb Natapov
2013-03-17 10:45 ` Jan Kiszka
2013-03-17 10:47 ` Gleb Natapov
2013-03-20 19:30 ` Marcelo Tosatti
2013-03-20 20:03 ` Marcelo Tosatti
2013-03-20 21:32 ` Gleb Natapov
2013-03-20 23:19 ` Marcelo Tosatti
2013-03-21 4:54 ` Gleb Natapov
2013-03-21 14:02 ` Marcelo Tosatti [this message]
2013-03-21 14:18 ` Gleb Natapov
2013-03-21 14:27 ` Zhang, Yang Z
2013-03-21 16:27 ` Gleb Natapov
2013-03-21 20:51 ` Marcelo Tosatti
2013-03-21 21:13 ` Gleb Natapov
2013-03-21 23:06 ` Marcelo Tosatti
2013-03-22 1:50 ` Zhang, Yang Z
2013-03-22 6:53 ` Gleb Natapov
2013-03-22 10:43 ` Marcelo Tosatti
2013-03-22 11:19 ` Gleb Natapov
2013-03-24 10:45 ` Zhang, Yang Z
2013-03-24 19:03 ` Gleb Natapov
2013-04-28 10:15 ` Jan Kiszka
2013-04-28 10:19 ` Gleb Natapov
2013-04-28 10:20 ` Jan Kiszka
2013-04-28 10:23 ` Gleb Natapov
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